A088627 Let 2n = r*s. Then a(n) = number of primes of the form r+s (r= 1 and s = 2n contributes 1 to the count if 2n+1 is prime).
1, 1, 2, 0, 2, 2, 0, 1, 2, 0, 2, 1, 0, 2, 4, 0, 1, 2, 0, 2, 4, 0, 1, 1, 0, 2, 1, 0, 2, 4, 0, 0, 2, 0, 4, 2, 0, 1, 4, 0, 2, 2, 0, 2, 3, 0, 0, 1, 0, 2, 4, 0, 1, 2, 0, 2, 2, 0, 1, 3, 0, 0, 2, 0, 4, 3, 0, 1, 3, 0, 1, 0, 0, 2, 3, 0, 2, 2, 0, 1, 2, 0, 1, 3, 0, 2, 2, 0, 1, 3, 0, 1, 1, 0, 4, 2, 0, 2, 4, 0, 1, 2, 0, 1, 8
Offset: 1
Keywords
Examples
a(9) = 2 18 = 1*18, 1+18= 19 and 18 = 2*9, 2+9 = 11, two primes arise.
Links
- T. D. Noe, Table of n, a(n) for n=1..10000
- M. Engelhardt, Number of Primes arising as Sum of a Factorization.
Crossrefs
Cf. A091350.
Extensions
More terms from Matthias Engelhardt, Jan 05 2004
More terms from David Wasserman, Aug 15 2005
Comments