A141099 Number of unordered pairs of odd nonprime numbers that sum to 2n.

1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 1, 2, 0, 2, 3, 0, 2, 3, 1, 2, 3, 3, 2, 4, 2, 3, 5, 1, 4, 6, 1, 5, 5, 3, 4, 7, 3, 4, 7, 4, 4, 9, 4, 5, 8, 4, 7, 9, 5, 6, 8, 6, 7, 10, 6, 6, 13, 5, 7, 13, 5, 10, 11, 8, 8, 11, 9, 10, 14, 9, 9, 16, 7, 12, 15, 8, 12, 15, 9, 10, 17, 14, 11, 16, 12, 12, 19, 11, 13, 19

Offset: 1

Author

T. D. Noe, Jun 02 2008, Jun 05 2008

Keywords

• nonn

Comments

See A141100 for pairs of odd composite numbers. We have a(n) > 0 except for the 8 values of 2n given in A046458.

Examples

			a(18)=3 because 36 = 1+35 = 9+27 = 15+21.
		

Links

• T. D. Noe, Table of n, a(n) for n=1..1000

Crossrefs

Cf. A141095, A141097.

Programs

Mathematica

Table[cnt=0; Do[If[ !PrimeQ[i] && !PrimeQ[2n-i], cnt++ ], {i,1,n,2}]; cnt, {n,100}]