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 A257644 #14 Oct 31 2023 17:52:40 %S A257644 1,3,8,14,24,32,48,58,77,93,115,129,163,179,207,235,271,291,336,358, %T A257644 406,442,482,508,576,610,656,700,762,794,874,908,977,1029,1087,1139, %U A257644 1239,1279,1343,1403,1501,1545,1649,1695,1785,1869,1945,1995,2129,2189 %N A257644 First differences of A264100. %C A257644 Cumulative sum of A007503, starting with 1. %H A257644 Reinhard Zumkeller, <a href="/A257644/b257644.txt">Table of n, a(n) for n = 0..10000</a> %o A257644 (PARI) alist(n)=my(x);vector(n,k,if(k==1,x=1,x+=sigma(k-1)+numdiv(k-1))) %o A257644 (Haskell) %o A257644 a257644 n = a257644_list !! n %o A257644 a257644_list = scanl (+) 1 a007503_list -- _Reinhard Zumkeller_, Nov 09 2015 %o A257644 (Python) %o A257644 from math import isqrt %o A257644 def A257644(n): return (-(s:=isqrt(n))*(s*(s+4)+5)+sum(((q:=n//w)+1)*(q+(w<<1)+4) for w in range(1,s+1))>>1)+1 # _Chai Wah Wu_, Oct 31 2023 %Y A257644 Cf. A000005, A000203, A007503, A264100. %K A257644 nonn %O A257644 0,2 %A A257644 _Franklin T. Adams-Watters_, Nov 05 2015