OFFSET
1,1
COMMENTS
p divides a(p) for prime p>3. p^2 divides a(p) for prime p=7. Nonprime n dividing a(n) are {1,15}.
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..210
FORMULA
a(n) = 1 + Sum_{i=1..n} Sum_{j=1..n} Sum_{k=1..n} i^(j+k).
a(n) = 1 + n^2 + Sum_{j=2..n} (j*(j^n - 1)/(j-1))^2.
MATHEMATICA
Table[Sum[(i(i^n-1)/(i-1))^2, {i, 2, n}] +n^2 +1, {n, 20}]
PROG
(PARI) vector(20, n, 1+n^2 + sum(j=2, n, (j*(j^n-1)/(j-1))^2)) \\ G. C. Greubel, Aug 02 2019
(Magma) [2] cat [1+n^2 + (&+[(j*(j^n-1)/(j-1))^2: j in [2..n]]): n in [1..20]]; // G. C. Greubel, Aug 02 2019
(Sage) [1+n^2 + sum((j*(j^n-1)/(j-1))^2 for j in (2..n)) for n in (1..20)] # G. C. Greubel, Aug 02 2019
(GAP) List([1..20], n-> 1 + n^2 + Sum([2..n], j-> (j*(j^n-1)/(j-1))^2) ); # G. C. Greubel, Aug 02 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Oct 17 2007
STATUS
approved