2,1

Table of n, a(n) for n=2..78.

2*5 = 10 can be expressed as the sum of two primes in two ways, 3+7 and 5+5, so a(5) = 3+5 = 8.

with(numtheory);

a:=n-> sum( (i)*( ((pi(i) - pi(i-1)) * (pi(2*n-i) - pi(2*n-i-1))) ), i = 1..n ); seq(a(k), k=1..100); # Wesley Ivan Hurt, Jan 20 2013

Cf. A045917, A187129, A186201.

Sequence in context: A078035 A295725 A132822 * A202818 A256679 A193997

Adjacent sequences: A185294 A185295 A185296 * A185298 A185299 A185300

nonn

N. J. A. Sloane, Mar 11 2011

approved