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 A321581 #28 Feb 06 2019 16:37:09 %S A321581 0,1,9,46656,1000000000000000000000000 %N A321581 a(n) is the sum of first n natural numbers raised to the product of first n natural numbers. %C A321581 The next term a(5) has 142 decimal digits. %F A321581 a(n) = (n*(n+1)/2)^(n!). %F A321581 a(n) = A000217(n)^A000142(n). %e A321581 a(3) = (1+2+3)^3! = 6^6 = 46656. %p A321581 [(n*(n+1)/2)^factorial(n)$n=0..5]; # _Muniru A Asiru_, Dec 20 2018 %t A321581 a[n_] := (n*(n + 1)/2)^n!; Array[a, 5] (* _Amiram Eldar_, Nov 13 2018 *) %o A321581 (PARI) a(n)=(n*(n+1)/2)^(n!); \\ _Andrew Howroyd_, Nov 13 2018 %o A321581 (GAP) List([1..5], n->(n*(n+1)/2)^(Factorial(n))); # _Stefano Spezia_, Nov 21 2018 %Y A321581 Cf. A000142, A000217, A067055. %K A321581 nonn,easy %O A321581 0,3 %A A321581 _Ayush Kumar Jha_, Nov 13 2018