A347744 Number of compositions (ordered partitions) of n into at most 2 prime parts (counting 1 as a prime).

1, 1, 2, 3, 3, 3, 3, 3, 4, 2, 3, 1, 4, 3, 5, 2, 4, 1, 6, 3, 6, 2, 5, 1, 8, 2, 5, 0, 4, 1, 8, 3, 6, 2, 7, 0, 8, 1, 5, 2, 6, 1, 10, 3, 8, 2, 7, 1, 12, 2, 8, 0, 6, 1, 12, 2, 6, 0, 7, 1, 14, 3, 7, 2, 10, 0, 12, 1, 6, 2, 10, 1, 14, 3, 11, 2, 10, 0, 14, 1, 10

Offset

0,3

Links

Table of n, a(n) for n=0..80.

Mathematica

Table[Length@Flatten[Permutations/@IntegerPartitions[n, 2, Join[{1}, Prime@Range@PrimePi@n]], 1], {n, 0, 80}] (* Giorgos Kalogeropoulos, Sep 12 2021 *)

Prog

(PARI) { a(n) = local(s(n) = if(n<2, 1, isprime(n))); if(n==0, 1, sum(i=1, n, s(i)*s(n-i))); } \\ Christian Krause, Dec 06 2022

Crossrefs

Cf. A001031, A008578, A096139, A280917, A341982, A347739, A347745.

Sequence in context: A025784 A035390 A092938 * A361197 A320110 A068953

Adjacent sequences: A347741 A347742 A347743 * A347745 A347746 A347747

Keyword

nonn

Author

Ilya Gutkovskiy, Sep 11 2021

Status

approved