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 A053242 #13 Oct 27 2023 22:00:45 %S A053242 20,21,49,50,56,57,79,80,108,109,132,133,145,146,155,170,171,177,178, %T A053242 201,230,231,253,254,260,277,278,289,290,307,308,341,347,348,376,382, %U A053242 383,405,406,412,413,424,425,437,438,467,495,496,548,549,555,570,585 %N A053242 Numbers n such that A053238(n) = 1. %H A053242 Reinhard Zumkeller, <a href="/A053242/b053242.txt">Table of n, a(n) for n = 1..10000</a> %p A053242 with(numtheory): f := [seq( `if`((sigma(i) > sigma(i+1)),i,print( )), i=1..5000)]; %p A053242 seq( `if`(f[i+1] - f[i] = 2,i,print( )), i=1..1000); %o A053242 (Haskell) %o A053242 import Data.List (elemIndices) %o A053242 a053242 n = a053242_list !! (n-1) %o A053242 a053242_list = map (+ 1) $ elemIndices 1 a053238_list %o A053242 -- _Reinhard Zumkeller_, Oct 16 2011 %Y A053242 Cf. A000203, A053226, A053238, A053239, A053240, A053241, A053243, A053244, A053245 (subsequence). %K A053242 nonn %O A053242 1,1 %A A053242 _Asher Auel_, Jan 10 2000