OFFSET
0,8
COMMENTS
Number of ordered ways of writing n as sum of three prime powers (1 excluded).
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Eric Weisstein's World of Mathematics, Prime Power
FORMULA
G.f.: (Sum_{k>=2} floor(1/omega(k))*x^k)^3.
EXAMPLE
a(7) = 3 because we have [3, 2, 2], [2, 3, 2] and [2, 2, 3].
MATHEMATICA
nmax = 70; CoefficientList[Series[(Sum[Floor[1/PrimeNu[k]] x^k, {k, 2, nmax}])^3, {x, 0, nmax}], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 29 2016
STATUS
approved