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 A035253 #12 Jun 07 2025 18:44:17 %S A035253 4,1,0,1,3,7,12,18,26,35,45,56,69,83,98,114,131,150,170,191,213,236, %T A035253 260,286,313,341,370,400,431,463,497,532,568,605,643,682,722,763,806, %U A035253 850,895,941,988,1036,1085,1135,1186,1239,1293,1348,1404,1461,1519,1578 %N A035253 Second differences are 2,2,1,2,1,1,2,1,1,1,2,1,1,1,1,2,1,1,1,1,1,2,.. (A035214). %F A035253 a(n) = A060432(n-1)+4+n*(n-7)/2. - _Chai Wah Wu_, Jun 07 2025 %o A035253 (Python) %o A035253 from math import isqrt %o A035253 def A035253(n): return (k:=(r:=isqrt(m:=n<<1))+int((m<<2)>(r<<2)*(r+1)+1)-1)*(k*(-k-3)+6*n-8)//6+(n*(n-5)>>1)+3 # _Chai Wah Wu_, Jun 07 2025 %Y A035253 Different from A005228. Cf. A035254, A060432. %K A035253 nonn,easy %O A035253 0,1 %A A035253 Robet Bronson (bob(AT)bronsons.com) %E A035253 More terms from _Chai Wah Wu_, Jun 07 2025