A069879 Number of pairs {i,j} with i different from j; 1<=i<=n; 1<= j <=n such that i+j is a prime number.

0, 2, 4, 8, 10, 14, 18, 22, 28, 36, 42, 50, 56, 62, 70, 80, 88, 96, 104, 112, 122, 134, 144, 156, 168, 180, 194, 208, 220, 234, 248, 262, 276, 292, 308, 326, 344, 362, 380, 400, 418, 438, 456, 474, 494, 514, 532, 550, 570, 590, 612, 636, 658, 682, 708, 734

Offset

1,2

Links

Table of n, a(n) for n=1..56.

Formula

a(n) = 2 * A071917(n). - Alois P. Heinz, Sep 29 2017

Maple

with(numtheory):
b:= proc(n) option remember; `if`(n=0, 0,
      b(n-1)+pi(2*n-1)-pi(n))
    end:
a:= n-> 2*b(n):
seq(a(n), n=1..70);  # Alois P. Heinz, Sep 29 2017

Mathematica

Table[2*Count[Subsets[Range[n], {2}], _?(PrimeQ[Total[#]]&)], {n, 50}] (* Harvey P. Dale, Jan 23 2015 *)

Crossrefs

Partial sums of 2*A060715(n).

Sequence in context: A034822 A300781 A050567 * A074330 A317626 A292550

Adjacent sequences: A069876 A069877 A069878 * A069880 A069881 A069882

Keyword

nonn

Author

Santi Spadaro, May 04 2002

Status

approved