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 A053240 #12 Oct 27 2023 22:00:45 %S A053240 5,20,21,29,34,49,50,56,57,65,70,79,80,94,99,108,109,123,132,133,145, %T A053240 146,154,155,170,171,177,178,198,200,201,227,230,231,239,244,253,254, %U A053240 259,260,274,277,278,280,289,290,304,307,308,310,327,332,340,341,347 %N A053240 n for which values not equal to 2 occur in the expansion of A053238. %H A053240 Reinhard Zumkeller, <a href="/A053240/b053240.txt">Table of n, a(n) for n = 1..10000</a> %p A053240 with(numtheory): f := [seq( `if`((sigma(i) > sigma(i+1)),i,print( )), i=1..5000)]; %p A053240 seq( `if`(f[i+1] - f[i] <> 2,i,print( )), i=1..1000); %o A053240 (Haskell) %o A053240 import Data.List (findIndices) %o A053240 a053240 n = a053240_list !! (n-1) %o A053240 a053240_list = map (+ 1) $ findIndices (/= 2) a053238_list %o A053240 -- _Reinhard Zumkeller_, Oct 16 2011 %Y A053240 Cf. A000203, A053226, A053238, A053239, A053241 (complement), A053242, A053243, A053244, A053245. %K A053240 nonn %O A053240 1,1 %A A053240 _Asher Auel_, Jan 10 2000