OFFSET
0,11
COMMENTS
Number of compositions (ordered partitions) into semiprimes (A001358).
LINKS
Eric Weisstein's World of Mathematics, Semiprime
FORMULA
G.f.: 1/(1 - Sum_{k>=2} floor(bigomega(k)/2)*floor(2/bigomega(k))*x^k).
EXAMPLE
a(10) = 3 because we have [4, 6], [6, 4] and [10].
MATHEMATICA
nmax = 44; CoefficientList[Series[1/(1 - Sum[Floor[PrimeOmega[k]/2] Floor[2/PrimeOmega[k]] x^k, {k, 2, nmax}]), {x, 0, nmax}], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 29 2016
STATUS
approved