A159260 Numbers k such that 1 + Sum_{i=1..k} 2^prime(i) is prime.
1, 2, 4, 5, 8, 43, 127, 251, 1903
Offset: 1
Keywords
Examples
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.
Programs
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Mathematica
s=1; Reap[Do[s=s+2^Prime[n]; If[PrimeQ[s], Sow[n]], {n,2000}]][[2,1]]
Comments