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 A109391 #5 Nov 03 2018 11:43:35
%S A109391 0,1,12,162,2560,46875,979776,23059204,603979776,17433922005,
%T A109391 550000000000,18830570260326,695455834963968,27561634699895023,
%U A109391 1166760716683591680,52547266845703125000,2508757194024499019776
%N A109391 a(n) = (n^(n+1))*(n + 1)/2 = A000217(n)*A000312(n).
%C A109391 The sum of all the terms of all A000312(n) sequences having exactly n terms all chosen from {1,2,...,n}. Partial sums are A109392.
%F A109391 a(n) = (n^(n+1))*(n + 1)/2.
%e A109391 a(2) = (2^(2+1))*(2 + 1)/2 = 8*3/2 = 12. Note that the 2^2 sequences 1, 1; 1, 2; 2, 1; 2, 2 have 1 + 1 + 1 + 2 + 2 + 1 + 2 + 2 = 12 as the sum of all their terms (each element of {1, 2, ... , n} occurs n^(n-1) times in each of the n positions of the n^n sequences and (1 + 2 + ... + n)*n*n^(n-1) = A000217(n)*A000312(n)).
%Y A109391 Cf. A000217 (triangular numbers), A000312 (n^n: endofunctions), A109392 (partial sums).
%K A109391 nonn
%O A109391 0,3
%A A109391 _Rick L. Shepherd_, Jun 26 2005