OFFSET
0,2
FORMULA
a(n) = ((2*n)^(n+1) - 1)/(2*n - 1).
MATHEMATICA
a[0] = 1; a[n_] := Sum[(2*n)^k, {k, 0, n}]; Array[a, 18, 0] (* Amiram Eldar, Dec 07 2021 *)
PROG
(PARI) a(n) = sum(k=0, n, (2*n)^k);
(PARI) a(n) = ((2*n)^(n+1)-1)/(2*n-1);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 07 2021
STATUS
approved