OFFSET
1,6
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
a(n) <= A001221(n).
a(n) = Sum_{p|n} A101264(p), where p is a prime. - Ridouane Oudra, Aug 25 2019
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = Sum_{k>=1} 1/A005384(k) (see A005384 for an estimate of this sum). - Amiram Eldar, Jun 03 2024
MAPLE
with(numtheory): A101264:=p-> pi(2*p+1)-pi(2*p): seq(add(A101264(p), p in factorset(n)), n=1..100); # Ridouane Oudra, Aug 25 2019
MATHEMATICA
Join[{0}, Table[Count[FactorInteger[n][[All, 1]], _?(PrimeQ[2#+1]&)], {n, 2, 110}]] (* Harvey P. Dale, Apr 05 2020 *)
PROG
(Magma) [0] cat [&+[#PrimesInInterval(2*p, 2*p+1):p in PrimeDivisors(n)]:n in [2..100]]; // Marius A. Burtea, Aug 25 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Feb 10 2009
STATUS
approved