OFFSET
1,2
COMMENTS
All powers are squares with the exception of 3^3 for a(2) and 6^9 for a(6). I conjecture these are the only nonsquare powers.
a(19) > 10^10. - Zak Seidov, Jul 06 2013
FORMULA
EXAMPLE
Considering 1 not to be prime and not to be composite, first composite is 4 which is 2^2. And the sum of the first four composites is 4 + 6 + 8 + 9 = 27 = 3^3.
MAPLE
# see A001597 for isA001597
for n from 1 do
if isA001597(A053767(n) ) then
print(n) ;
end if;
end do: # R. J. Mathar, Jul 08 2013
PROG
(PARI) : n=10^7; v=vector(n); i=0; for(a=2, n, if(isprime(a), next, i++; v[i]=a)); k=0; for(j=1, i, k=k+v[j]; if(ispower(k, , &n), print1([k, n, j], " ")))
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robin Garcia, Jul 04 2013
EXTENSIONS
a(11) - a(18) from Zak Seidov, Jul 06 2013
STATUS
approved