login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A286219 Number of partitions of n into parts with an even number of prime divisors (counted with multiplicity). 5
1, 1, 1, 1, 2, 2, 3, 3, 4, 5, 7, 7, 9, 10, 13, 15, 19, 20, 25, 28, 34, 38, 46, 50, 61, 69, 81, 89, 105, 116, 137, 152, 175, 194, 226, 250, 288, 318, 363, 403, 462, 508, 577, 637, 721, 796, 900, 988, 1113, 1228, 1378, 1515, 1696, 1860, 2080, 2287, 2546, 2791, 3106, 3402, 3779 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..10000

Eric Weisstein's World of Mathematics, Prime Factor

Index entries for related partition-counting sequences

FORMULA

G.f.: Product_{k>=1} 1/(1 - x^A028260(k)).

EXAMPLE

a(8) = 4 because we have [6, 1, 1], [4, 4], [4, 1, 1, 1, 1] and [1, 1, 1, 1, 1, 1, 1, 1].

MAPLE

with(numtheory):

a:= proc(n) option remember; `if`(n=0, 1, add(a(n-j)*add(

      `if`(bigomega(d)::odd, 0, d), d=divisors(j)), j=1..n)/n)

    end:

seq(a(n), n=0..80);  # Alois P. Heinz, May 04 2017

MATHEMATICA

nmax = 60; CoefficientList[Series[Product[1/(1 - Boole[EvenQ[PrimeOmega[k]]] x^k), {k, 1, nmax}], {x, 0, nmax}], x]

CROSSREFS

Cf. A028260, A087153, A285798, A286218.

Sequence in context: A064650 A174619 A130083 * A117357 A029020 A035380

Adjacent sequences:  A286216 A286217 A286218 * A286220 A286221 A286222

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, May 04 2017

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 25 19:25 EDT 2019. Contains 323576 sequences. (Running on oeis4.)