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

1,15

Comments

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

Links

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

Example

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

Mathematica

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

Crossrefs

Cf. A141095, A141097.

Sequence in context: A204329 A111565 A299761 * A127710 A137510 A247303

Adjacent sequences: A141096 A141097 A141098 * A141100 A141101 A141102

Keyword

nonn

Author

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

Status

approved