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 A072858 Primes p such that 1/p has a square "period length". 1
 2, 3, 5, 17, 101, 163, 257, 577, 883, 1297, 1801, 3137, 3529, 5477, 7057, 7351, 8929, 9397, 11831, 12101, 13457, 13553, 14401, 15361, 15377, 15973, 19841, 20809, 21401, 21601, 23549, 24337, 25601, 29401, 30977, 33301, 33751, 33857, 38237 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE The period length of 1/17 = 0.05882352941176470588... is 16 = 4^2, hence 17 is in the sequence. The period length of 1/163 = 81 = 9^2. 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 Cf. A002371. Sequence in context: A065952 A308316 A089983 * A276629 A218086 A291049 Adjacent sequences:  A072855 A072856 A072857 * A072859 A072860 A072861 KEYWORD easy,nonn AUTHOR Benoit Cloitre, Jul 26 2002 STATUS approved

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Last modified October 20 15:46 EDT 2019. Contains 328267 sequences. (Running on oeis4.)