login
A321581
a(n) is the sum of first n natural numbers raised to the product of first n natural numbers.
0
0, 1, 9, 46656, 1000000000000000000000000
OFFSET
0,3
COMMENTS
The next term a(5) has 142 decimal digits.
FORMULA
a(n) = (n*(n+1)/2)^(n!).
a(n) = A000217(n)^A000142(n).
EXAMPLE
a(3) = (1+2+3)^3! = 6^6 = 46656.
MAPLE
[(n*(n+1)/2)^factorial(n)$n=0..5]; # Muniru A Asiru, Dec 20 2018
MATHEMATICA
a[n_] := (n*(n + 1)/2)^n!; Array[a, 5] (* Amiram Eldar, Nov 13 2018 *)
PROG
(PARI) a(n)=(n*(n+1)/2)^(n!); \\ Andrew Howroyd, Nov 13 2018
(GAP) List([1..5], n->(n*(n+1)/2)^(Factorial(n))); # Stefano Spezia, Nov 21 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Ayush Kumar Jha, Nov 13 2018
STATUS
approved