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 A083215 #11 Feb 16 2025 08:32:49
%S A083215 3,12,37,86,185,328,549,834,1225,1776,2427,3278,4303,5464,6827,8470,
%T A083215 10417,12552,15031,17800,20793,24190,27925,32108,36861,42012,47471,
%U A083215 53356,59569,66236,73983,82236,91141,100454,110735,121456,132917
%N A083215 a(n) = 1 + Sum(prime(i)*(2*i-1): 1<=i<=n).
%H A083215 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FigurateNumber.html">Figurate Number</a>.
%t A083215 nxt[{n_, a_}] := {n + 1, a + Prime[n + 1] (2 n + 1)}; NestList[nxt,{1,2},50][[All,2]]+1 (* _Harvey P. Dale_, Jul 05 2018 *)
%o A083215 (PARI) a(n) = 1 + sum(i=1, n, prime(i)*(2*i-1)); \\ _Michel Marcus_, Jan 22 2022
%Y A083215 Cf. A002412.
%Y A083215 Equals 1 + A316322(n).
%K A083215 nonn
%O A083215 1,1
%A A083215 _Reinhard Zumkeller_, Jun 01 2003
%E A083215 Definition corrected by _Harvey P. Dale_, Jul 03 2018