

A302301


Number of ways to write n as a sum of two distinct semiprimes.


0



0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 1, 2, 1, 1, 0, 1, 2, 2, 1, 1, 1, 2, 2, 3, 2, 0, 1, 3, 3, 2, 1, 3, 3, 2, 2, 4, 3, 2, 1, 4, 5, 3, 2, 1, 2, 3, 2, 5, 3, 2, 2, 5, 6, 6, 1, 3, 5, 3, 3, 4, 4, 3, 2, 6, 7, 5, 3, 3, 3, 4, 3, 5, 5, 3, 2, 7, 7, 2, 4
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OFFSET

1,19


LINKS

Table of n, a(n) for n=1..86.
Index entries for sequences related to partitions


FORMULA

a(n) = Sum_{i=1..floor((n1)/2)} [Omega(i) = 2] * [Omega(ni) = 2], where Omega = A001222 and [] is the Iverson bracket.


EXAMPLE

a(19) = 2; 19 = 15+4 = 10+9.


MATHEMATICA

Table[Sum[KroneckerDelta[PrimeOmega[i], 2] KroneckerDelta[PrimeOmega[n  i], 2], {i, Floor[(n  1)/2]}], {n, 100}]


PROG

(PARI) a(n) = sum(i=1, (n1)\2, (bigomega(i)==2)*(bigomega(ni)==2)); \\ Michel Marcus, Apr 08 2018


CROSSREFS

Cf. A001222, A001358, A072931.
Sequence in context: A068914 A090824 A264620 * A277264 A259538 A099314
Adjacent sequences: A302298 A302299 A302300 * A302302 A302303 A302304


KEYWORD

nonn,easy


AUTHOR

Wesley Ivan Hurt, Apr 04 2018


STATUS

approved



