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A347744 Number of compositions (ordered partitions) of n into at most 2 prime parts (counting 1 as a prime). 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
LINKS
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
Sequence in context: A025784 A035390 A092938 * A361197 A320110 A068953
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Sep 11 2021
STATUS
approved

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Last modified June 18 21:09 EDT 2024. Contains 373487 sequences. (Running on oeis4.)