A345238 - OEIS

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A345238

a(n) is the number of primes of the form prime(n)+2^k for 2^k < prime(n).

1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 2, 2, 2, 1, 1, 2, 0, 3, 3, 2, 1, 0, 1, 2, 2, 2, 2, 2, 0, 2, 2, 1, 0, 4, 1, 1, 3, 1, 1, 3, 1, 3, 2, 2, 1, 1, 2, 1, 2, 1, 3, 1, 2, 0, 1, 3, 0, 2, 3, 1, 1, 2, 2, 2, 1, 2, 3, 2, 1, 0, 2, 2, 1, 2, 0, 2, 3, 2, 0, 2, 1, 3, 1, 2, 1, 2, 2, 1, 3, 1, 2, 3, 3, 2, 1, 1, 2, 1

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,5

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

a(5) = 2 because prime(5) = 11 and 11+2^1 = 13 and 11+2^3 = 19 are prime.

MAPLE

f:= proc(n) local p, k;

p:= ithprime(n);

nops(select(isprime, [seq(p+2^k, k=1..ilog2(p))]))

end proc: