This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A128948 #18 Oct 10 2019 10:20:20
%S A128948 3,17,73,101,137,163,257,353,449,577,641,751,757,883,1297,1409,1801,
%T A128948 3137,3529,5477,7057,7351,8929,9397,10753,11831,12101,13457,13553,
%U A128948 14401,15361,15377,15973,18523,19841,20809,21401,21601,23549,24001,24337
%N A128948 Primes p for which the period length of 1/p is a perfect power, A001597.
%C A128948 Number of primes p < 10^n whose period length of 1/p is a perfect power: 1,3,14,24,78,173,461,1190,3235,8933,....
%C A128948 The primes modulo any integer do not seem to be equally distributed.
%H A128948 Ray Chandler & Robert G. Wilson v, <a href="/A128948/b128948.txt">Table of n, a(n) for n = 1..30000</a>
%H A128948 <a href="/index/1#1overn">Index entries for sequences related to decimal expansion of 1/n</a>
%e A128948 The prime 73 has a period of 8 = 2^3 which is a member of A001597, hence is a member of this sequence.
%t A128948 lst = {3}; p = 1; While[p < 10^8, p = NextPrime@p; If[GCD @@ Last /@ FactorInteger@ MultiplicativeOrder[10, p] > 1, AppendTo[lst, p]; Print@p]]; lst (* _Ray Chandler_, May 11 2007 *)
%Y A128948 Cf. A001597, A072859, A072982.
%K A128948 base,nonn
%O A128948 1,1
%A A128948 _Robert G. Wilson v_, May 05 2007
%E A128948 Correction (3 is a member of the sequence) from Ray Chandler, May 11 2007
%E A128948 B-file corrected by _Ray Chandler_, Oct 23 2011