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%I #24 Nov 18 2023 22:24:15
%S 2,3,5,17,101,163,257,577,883,1297,1801,3137,3529,5477,7057,7351,8929,
%T 9397,11831,12101,13457,13553,14401,15361,15377,15973,19841,20809,
%U 21401,21601,23549,24337,25601,29401,30977,33301,33751,33857,38237
%N Primes p such that the period of the decimal expansion of 1/p is a square.
%H Amiram Eldar, <a href="/A072858/b072858.txt">Table of n, a(n) for n = 1..10000</a>
%e The period of 1/17 = 0.05882352941176470588... is 16 = 4^2, hence 17 is in the sequence.
%e The period of 1/163 = 81 = 9^2.
%t Select[Prime[Range[4000]], IntegerQ @ Sqrt[Length[RealDigits[1/#][[1, 1]]]] &] (* _Amiram Eldar_, May 21 2022 *)
%o (PARI) (a(n)=if(n<4,n==2,znorder(Mod(10, prime(n))))); for(n=1,1000,if(issquare(a(n))==1,print1(prime(n),","))) /* Thanks to _Michael Somos_ for improvement of the PARI program */
%Y Cf. A002371.
%K easy,nonn,base
%O 1,1
%A _Benoit Cloitre_, Jul 26 2002
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