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A025148 Number of partitions of n into distinct parts >= 3. 5
1, 0, 0, 1, 1, 1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 9, 10, 12, 15, 17, 20, 24, 28, 32, 38, 44, 51, 59, 68, 78, 91, 103, 118, 136, 155, 176, 201, 228, 259, 294, 332, 375, 425, 478, 538, 607, 681, 764, 858, 961, 1075, 1203, 1343, 1499, 1673, 1863, 2073, 2308, 2564, 2847, 3161, 3504 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,8

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..1000

FORMULA

G.f.: Product_{k=3..inf} (1+x^k).

a(n) = A096749(n+2). - R. J. Mathar, Jul 31 2008

G.f.: sum(n>=0, x^(n*(n+5)/2) / prod(k=1..n, 1-x^k) ); special case of g.f. for partitions into distinct parts >= L, sum(n>=0, x^(n*(n+2*L-1)/2) / prod(k=1..n, 1-x^k) ). - Joerg Arndt, Mar 24 2011

G.f.: sum(n>=2, x^(n*(n+1)/2-3) / prod(k=1..n-2, 1-x^k) ), a special case of the g.f. for partitions into distinct parts >= L, sum(n>=L-1, x^(n*(n+1)/2-L*(L-1)/2) / prod(k=1..n-(L-1), 1-x^k) ). - Joerg Arndt, Mar 27 2011

a(n) + a(n+1) + a(n+2) + a(n+3) = A000009(n+3). - Vaclav Kotesovec, Oct 22 2015

a(n) ~ 1/4 * A000009(n). - Vaclav Kotesovec, Oct 22 2015

MAPLE

with(combstruct) ; sys := {L = PowerSet(Sequence(Z, card>2)) }; seq( count([L, sys], size=i), i=0..56 ); # Zerinvary Lajos, Mar 08 2007

A025148 := proc(n) mul(1+x^k, k=3..n+1) ; expand(%) ; coeftayl(%, x=0, n) ; end proc: # R. J. Mathar, Mar 28 2011

# third Maple program:

b:= proc(n, i) option remember;

      `if`(n=0, 1, `if`((i-2)*(i+3)/2<n, 0,

       add(b(n-i*j, i-1), j=0..min(1, n/i))))

    end:

a:= n-> b(n$2):

seq(a(n), n=0..100);  # Alois P. Heinz, Feb 07 2014

MATHEMATICA

d[n_] := Select[IntegerPartitions[n], Max[Length /@ Split@#] == 1 && Min[#] >= 3 &]; Table[d[n], {n, 16}] (* strict partitions, parts >= 3 *)

Table[Length[d[n]], {n, 40}] (* A025148 for n >= 1 *)

(* Clark Kimberling, Mar 07 2014 *)

b[n_, i_] := b[n, i] = If[n==0, 1, If[(i-2)*(i+3)/2<n, 0, Sum[b[n-i*j, i-1], {j, 0, Min[1, n/i]}]]]; a[n_] := b[n, n]; Table[a[n], {n, 0, 100}] (* Jean-Fran├žois Alcover, Oct 22 2015, after Alois P. Heinz *)

CROSSREFS

Cf. A025147.

Sequence in context: A185227 A217569 A026823 * A096749 A036821 A237980

Adjacent sequences:  A025145 A025146 A025147 * A025149 A025150 A025151

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified May 31 08:09 EDT 2020. Contains 334747 sequences. (Running on oeis4.)