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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. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified December 12 13:56 EST 2018. Contains 318063 sequences. (Running on oeis4.)