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 A068983 #12 Aug 10 2021 21:12:00
%S A068983 0,2,23,255,3260,49196,867699,17604595,404662204,10401033404,
%T A068983 295672787215,9211294233871,312080173805324,11423999821072140,
%U A068983 449316582527563515,18896039733447227131,846135945932355895308,40192537618855187742732,2018612071634068368034711
%N A068983 a(n) = Sum_{k=0..n} (k^k-k!).
%C A068983 a(n) = number of non-injective functions [k]->[k] for 1<=k<=n.
%F A068983 a(n) = Sum_{k=0..n} (k^k-k!).
%F A068983 a(n) = A062970(n) - A003422(n+1). - _Alois P. Heinz_, Aug 10 2021
%e A068983 a(4) = 255 because (1^1-1!)+(2^2-2!)+(3^3-3!)+(4^4-4!) = 255.
%t A068983 Accumulate[Table[n^n-n!,{n,20}]] (* _Harvey P. Dale_, Aug 21 2011 *)
%Y A068983 Cf. A003422, A062970, A036679.
%K A068983 easy,nonn
%O A068983 1,2
%A A068983 _Darrell Minor_, Apr 02 2002