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 A178985 #37 May 09 2021 07:54:04
%S A178985 3,19,11,227,1019,269201,186023729,457933343698297657,
%T A178985 2267602862220213494836920572800947269169358383491,
%U A178985 3510117420185552058703020362961660520827436011216742688744177
%N A178985 Primes of the form 3^k mod 2^k, in the order in which they are found.
%C A178985 Can it be shown that this is always an increasing sequence?
%C A178985 {a(n)} is an increasing sequence because {a(n)} is a subsequence of the integer sequence {b(n)} = (fractional part of (3/2)^n without the decimal point)/5^n = A204544(n) / 5^n = prime terms of A002380. - _Michel Lagneau_, Jan 25 2012
%C A178985 Corresponding n: 3, 5, 7, 9, 11, 20, 28, 62, 161, 204, 471, 505, 881, 1810, 1812, 2506, 3321, ... - _Eric Chen_, Jun 13 2018
%H A178985 Eric Chen, <a href="/A178985/b178985.txt">Table of n, a(n) for n = 1..17</a>
%t A178985 f[n_] := PowerMod[3, n, 2^n]; Select[f@ Range@ 300, PrimeQ]
%Y A178985 Cf. A002380, A007520, A204544.
%K A178985 nonn
%O A178985 1,1
%A A178985 _Juri-Stepan Gerasimov_, Jan 03 2011