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 A069876 #18 Feb 10 2025 11:18:17
%S A069876 1,13,405,23058,2078375,271739011,48574262275,11373936899396,
%T A069876 3377498614484589,1240006139651007925,551449374186192949841,
%U A069876 292093390490112799117190,181694111127303339553250275,131144830297438122797495823519,108709456000518111261404495694375
%N A069876 a(n) = (k-n+1)^n + (k-n+2)^n + ... + (k-1)^n + k^n, where k = n(n+1)/2.
%C A069876 Sum of next n n-th powers.
%e A069876 a(1) = 1^1 = 1; a(2) = 2^2 + 3^2 = 13; a(3) = 4^3 + 5^3 + 6^3 = 405; a(4) = 7^4 + 8^4 + 9^4 + 10^4 = 23058.
%t A069876 i1 := n(n-1)/2+1; i2 := n(n-1)/2+n; Table[Sum[i^n, {i, i1, i2}], {n, 20}]
%o A069876 (Python)
%o A069876 def A069876(n): return sum(((n*(n+1)>>1)-i)**n for i in range(n)) # _Chai Wah Wu_, Feb 10 2025
%Y A069876 Cf. A072474 (for squares), A075664 - A075671 (3rd to 10th powers).
%K A069876 nonn
%O A069876 1,2
%A A069876 _Amarnath Murthy_, Apr 25 2002
%E A069876 More terms from Larry Reeves (larryr(AT)acm.org) and _Zak Seidov_, Sep 24 2002