login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A341495 Number of partitions of n into an odd number of parts such that the set of even parts has only one element. 5
0, 0, 1, 0, 2, 1, 5, 2, 9, 5, 17, 9, 30, 16, 49, 26, 78, 43, 122, 67, 184, 101, 272, 151, 397, 222, 567, 320, 802, 454, 1121, 637, 1545, 884, 2112, 1214, 2863, 1651, 3842, 2227, 5123, 2979, 6782, 3957, 8913, 5218, 11648, 6840, 15136, 8914, 19555, 11552, 25143 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..1000

Cristina Ballantine and Mircea Merca, Combinatorial proofs of two theorems related to the number of even parts in all partitions of n into distinct parts, Ramanujan J., 54:1 (2021), 107-112.

FORMULA

G.f.: (P(x,1) - P(x,-1))/2 where P(x,c) = (Sum_{k>=1} c*x^(2*k)/(1-c*x^(2*k))) / (Product_{k>=1} 1-c*x^(2*k-1)).

a(n) = A090867(n) - A341494(n).

EXAMPLE

The a(2) = 1 partition is: 2.

The a(4) = 2 partitions are: 4, 1+1+2.

The a(5) = 1 partition is: 1+2+2.

The a(6) = 5 partitions are: 6, 1+1+4, 1+2+3, 2+2+2, 1+1+1+1+2.

MATHEMATICA

P[n_, c_] := c*Sum[x^(2k)/(1 - c*x^(2k)) + O[x]^n, {k, 1, n/2}]/

Product[1 - c*x^(2k - 1) + O[x]^n, {k, 1, n/2}];

CoefficientList[(P[100, 1] - P[100, -1])/2, x] (* Jean-François Alcover, May 24 2021, from PARI code *)

PROG

(PARI)

P(n, c)={c*sum(k=1, n\2, x^(2*k)/(1-c*x^(2*k)) + O(x*x^n))/prod(k=1, n\2, 1-c*x^(2*k-1) + O(x*x^n))}

seq(n)={Vec(P(n, 1) - P(n, -1), -(n+1))/2}

CROSSREFS

Cf. A090867, A341494, A341496, A341497.

Sequence in context: A205377 A082010 A318972 * A337943 A275213 A113176

Adjacent sequences: A341492 A341493 A341494 * A341496 A341497 A341498

KEYWORD

nonn

AUTHOR

Andrew Howroyd, Feb 13 2021

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 6 16:43 EST 2023. Contains 360110 sequences. (Running on oeis4.)