OFFSET
1,2
COMMENTS
EXAMPLE
1 is here because 1 + 2^2 = 5 is prime.
2 is here because 1 + 2^2 + 2^3 = 13 is prime.
4 is here because 1 + 2^2 + 2^3 + 2^5 + 2^7 = 173 is prime.
5 is here because 1 + 2^2 + 2^3 + 2^5 + 2^7 + 2^11 = 2111 is prime.
MATHEMATICA
s=1; Reap[Do[s=s+2^Prime[n]; If[PrimeQ[s], Sow[n]], {n, 2000}]][[2, 1]]
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Apr 07 2009
STATUS
approved