OFFSET
1,2
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
KEYWORD
nonn
AUTHOR
Santi Spadaro, May 04 2002
STATUS
approved