Does the number 31 hold special meaning in Robert Heinlein's Starship Troopers?

Question

First, there's the 31 ways to get kicked out:

About the only thing we noticed, if we noticed anything, was what we called "the thirty-one ways to crash land." ... The "crash landings" were a worn-out joke, like "reveille oil" and "tent jacks" . . . they were the thirty-one capital offenses.

Then, there's form 31:

"Uh, this assumes that Lieutenant Silva is an efficient officer — "
"Hummmph! Mister, for your information, 'Quick' Silva has an unbroken string of 'Excellent — Recommended for Promotion' on his Form Thirty-One."

...

Third, you might come through all right . . . but get a downcheck on your Form Thirty-One from your examiner, namely me.

Finally, at the end, they have 31 seconds til blast off:

"Right away, Father." I gave him a quick hug, let the Navy drop crew seal us in. The shakes didn't start up again. Shortly I was able to report: "Bridge! Rico's Roughnecks . . . ready for drop!"
"Thirty-one seconds, Lieutenant." She added, "Good luck, boys! This time we take 'em !"

It may be nothing, but it seems like an odd random number to keep popping up.

Answer 1

This is a comment on babou's answer, in response to his suggestion to check the magazine serial. I am posting it as an answer because it's too long for a comment. Meanwhile, in the unlikely event that babou finds anything herein that would be a useful addition to his answer, he is welcome to copy it. Personally, I don't see the relevance of the magazine serial to the OP's question. I don't know how the magazine version is related to either the published book or the manuscript submitted to Scribner's, but my uneducated guess is that the magazine version was created by abridging one of the full-length versions to fit the space limitations of the magazine.

The answer is that "thirty-one capital offenses" and "thirty-one seconds" are in the magazine serial, "Form Thirty-One" is not. Form Thirty-One is mentioned in section 13 of the book Starship Troopers; sections 12 & 13 of the book are condensed into one section (section XI) in the serial, and the whole part where Form Thirty-One comes up is missing.

This is from "Starship Soldier" (first of two parts) in The Magazine of Fantasy and Science Fiction, October 1959 (available at the Internet Archive), p. 141, column 1:

Before church call every Sunday they lined us up and read aloud the disciplinary articles of the Laws and Regulations of the Military Forces. They were posted, too, outside the orderly tent. Nobody paid much mind. About the only thing we noticed was what we called "the thirty-one ways to crash land," the thirty-one capital offenses. Now and then somebody boasted of having found a thirty-second way—something preposterous and usually obscene.

And this is from the second part, in The Magazine of Fantasy and Science Fiction, November 1959 (available at the Internet Archive), p. 94, column 2:

"Thirty-one seconds, Lieutenant" She added, "Good luck, boys! This time we're going to take 'em!"

Answer 2

Heinlein started his career as an SF author at the age of 31.

Starship Trooper ended the first part of his career, when he was writing the novels of his juvenile series for Scribner. Starship Trooper was not accepted by Scribner, and Heinlein took the opportunity to reorient his work, rather than remain a "leading writer of children's books". The book was published by Putnam.

It is possible that he chose then to include these hints into the first book of his new career as a reminder. It might be interesting to look at the original manuscript submitted to Scribner to see whether the references to number 31 were there initially. But I do not even know whether this manuscript still exists.

[added after 5 months]

Actually the novel was first published in 1959 in "The Magazine of Fantasy & Science Fiction" as a serial called "Starship Soldier". So it might be worth looking at that serial, that is certainly available somewhere, to check whether it already contains these references to the number 31. According to Wikipedia, it is in the issues from October and November 1959. Who inherited that, is old enough, or has access to the library of Congress - and the time to check?