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 A053247 #11 Oct 27 2023 22:00:45 %S A053247 2,7,11,7,22,24,7,34,41,14,48,40,18,68,71,21,49,75,38,102,92,100,103, %T A053247 47,110,96,50,138,140,15,103,134,78,195,161,6,116,194,70,182,140,72, %U A053247 234,178,56,156,227,76,229,218,226,276,160,260,162,26,252,280,74,224 %N A053247 Second differences of sigma(n) that are positive. %H A053247 Harvey P. Dale, <a href="/A053247/b053247.txt">Table of n, a(n) for n = 1..1000</a> %F A053247 a(n) = A053223(A053228(n)) %p A053247 with (numtheory): f := [seq( sigma(i+2) - sigma(i+1) - (sigma(i+1) - sigma(i)), i=1..200)]; %p A053247 seq(`if`(f[i] > 0,f[i],print( )), i=1..200); %t A053247 Select[Differences[DivisorSigma[1,Range[150]],2],#>0&] (* _Harvey P. Dale_, May 10 2012 *) %Y A053247 Cf. A000203, A053223, A053248. %K A053247 nonn %O A053247 1,1 %A A053247 _Asher Auel_, Jan 11 2000