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 A112984 #9 Jul 11 2021 14:32:40 %S A112984 4,10,16,28,36,50,56,76,82,106,116,120,122,134,144,162,172,176,188, %T A112984 190,204,216,218,232,236,244,248,254,256,262,274,280,290,296,298,300, %U A112984 324,334,336,344,352,364,372,396,404,406,414,426,438,452,456,474,476,484 %N A112984 Numbers k such that 2^k mod k-1 is odd. %t A112984 Select[ 2Range[250], OddQ[ PowerMod[2, #, #-1]] &] (* _Robert G. Wilson v_, Oct 10 2005 *) %Y A112984 Cf. A112983, A015911. %K A112984 nonn %O A112984 1,1 %A A112984 _Paul Barry_, Oct 08 2005 %E A112984 More terms from _Robert G. Wilson v_, Oct 10 2005