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A286227 Number of compositions (ordered partitions) of n into parts with an even number of prime divisors (counted with multiplicity). 2
1, 1, 1, 1, 2, 3, 5, 7, 10, 15, 24, 36, 53, 78, 118, 179, 271, 405, 605, 907, 1366, 2055, 3086, 4628, 6948, 10440, 15689, 23560, 35371, 53110, 79771, 119821, 179958, 270243, 405833, 609495, 915394, 1374780, 2064647, 3100680, 4656676, 6993575, 10503180, 15773877, 23689467, 35577360 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,5
LINKS
Eric Weisstein's World of Mathematics, Prime Factor
FORMULA
G.f.: 1/(1 - Sum_{k>=1} x^A028260(k)).
EXAMPLE
a(6) = 5 because we have [6], [4, 1, 1], [1, 4, 1], [1, 1, 4] and [1, 1, 1, 1, 1, 1].
MATHEMATICA
nmax = 45; CoefficientList[Series[1/(1 - Sum[Boole[EvenQ[PrimeOmega[k]]] x^k, {k, 1, nmax}]), {x, 0, nmax}], x]
CROSSREFS
Sequence in context: A018133 A261081 A116975 * A134792 A300795 A033068
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, May 04 2017
STATUS
approved

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Last modified May 29 22:36 EDT 2024. Contains 372954 sequences. (Running on oeis4.)