OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
The period of 1/17 = 0.05882352941176470588... is 16 = 4^2, hence 17 is in the sequence.
The period of 1/163 = 81 = 9^2.
MATHEMATICA
Select[Prime[Range[4000]], IntegerQ @ Sqrt[Length[RealDigits[1/#][[1, 1]]]] &] (* Amiram Eldar, May 21 2022 *)
PROG
(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 */
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Benoit Cloitre, Jul 26 2002
STATUS
approved