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 A248755 #10 Feb 16 2025 08:33:23
%S A248755 2,2,1,4,3,3,4,2,5,4,6,5,4,5,11,3,15,6,5,3,5,6,11,13,5,4,9,27,11,10,8,
%T A248755 7,23,13,20,12,14,10,41,28,12,4,36,4,15,13,27,8,15,11,13,24,5,51,8,65,
%U A248755 36,8,13,47,36,42,31,20,13,52,42,6,87,16,30,89,15,7,36,95,6,17,34,10
%N A248755 a(n) is the number of iterations for the Lucas-Lehmer sequence A003010 (mod p_n) to enter a loop, where p_n is the n-th prime number A000040(n).
%C A248755 The Lucas-Lehmer sequence is used to test for Mersenne primes (A001348), but this is irrelevant for this sequence.
%H A248755 GIMPS, <a href="http://www.mersenne.org/"> Great Internet Mersenne Prime Search</a>
%H A248755 Eric W. Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Lucas-LehmerTest.html"> Lucas-Lehmer Test</a>
%H A248755 Wikipedia, <a href="http://en.wikipedia.org/wiki/Lucas%E2%80%93Lehmer_primality_test"> Lucas-Lehmer primality test</a>
%e A248755 a(4) is 4 because p_4 = 7, and the sequence A003010 (mod 7) becomes -> 4, 0, 5, 2, 2, 2, 2, 2, 2, .... The term 2 which is the first term of an infinite loop is at position 4.
%t A248755 f[n_] := -1 + Length@ NestWhileList[ Mod[#^2 - 2, Prime[n]] &, 4, UnsameQ[##] &, {2, Infinity}]; Array[f, 80]
%Y A248755 Cf. A003010, A001348, A095847, A000043.
%K A248755 nonn,easy
%O A248755 1,1
%A A248755 _Robert G. Wilson v_, Oct 13 2014