OFFSET
1,3
COMMENTS
As n increases, sum k(n) for i=1 to n / sum n for i=1 to n tends to 1/4. All values in b152414 verified and primes certified using PFGW from Primeform group.
Contribution from Pierre CAMI, Dec 04 2008: (Start)
for n even sum k(2*n) for i=1 to n / sum 2*n for i=1 to n tends to log(2)/4.
for n odd sum k(2*n+1) for i=0 to n / sum 2*n+1 for i=1 to n tends to 1/2-log(2)/4.
(End)
LINKS
Pierre CAMI, Table of n, a(n) for n=1..4000
EXAMPLE
1*2^1*(2^1-1)+1=3 is prime so k(1)=1.
1*2^2*(2^2-1)-1=11 is prime, as well as 13, so k(2)=1.
2*2^3*(2^3-1)+1=113 is prime so k(3)=2.
PROG
(PARI) a(n) = {k = 1; while (! (isprime(k*2^n*(2^n-1)+1) || isprime(k*2^n*(2^n-1)-1)), k++); return (k); } \\ Michel Marcus, Mar 07 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Dec 03 2008
STATUS
approved