

A008951


Array read by columns: number of partitions of n into parts of 2 kinds.


14



1, 1, 1, 2, 2, 3, 4, 1, 5, 7, 2, 7, 12, 5, 11, 19, 9, 1, 15, 30, 17, 2, 22, 45, 28, 5, 30, 67, 47, 10, 42, 97, 73, 19, 1, 56, 139, 114, 33, 2, 77, 195, 170, 57, 5, 101, 272, 253, 92, 10, 135, 373, 365, 147, 20, 176, 508, 525, 227, 35, 1, 231, 684, 738, 345, 62, 2, 297
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OFFSET

0,4


COMMENTS

FineRiordan array S_n(m)=a(n,m) with extra row for n=0 added.
Row n of this triangle has length floor(1/2 + sqrt(2*(n+1))), n>=0. This is sequence A002024(n+1)=[1,2,2,3,3,3,4,4,4,4,5,5,5,5,5,6,6,6,6,6,6,...].
Written as triangle this becomes A103923.
a(n,m) gives also the number of partitions of nt(m), where t(m):=A000217(m) (triangular numbers), with two kinds of parts 1,2,..m. See the column o.g.f.'s in table A103923.
In general, column m is asymptotic to exp(Pi*sqrt(2*n/3)) * 6^(m/2) * n^((m2)/2) / (4*sqrt(3) * m! * Pi^m), equivalently to 6^(m/2) * n^(m/2) / (m! * Pi^m) * p(n), where p(n) is the partition function A000041.  Vaclav Kotesovec, Aug 28 2015


REFERENCES

H. Gupta et al., Tables of Partitions. Royal Society Mathematical Tables, Vol. 4, Cambridge Univ. Press, 1958, p. 90.
J. Riordan, Combinatorial Identities, Wiley, 1968, p. 199.


LINKS

Alois P. Heinz, Columns n = 0..500, flattened
William K. Keith, Restricted kcolor partitions, arXiv preprint arXiv:1408.4089 [math.CO], 2014.
Wolfdieter Lang, First 20 rows and comments.


FORMULA

Riordan gives formula.
a(n, m) = sum over partitions of n of product(k[j], j=1..m), with k[j]=number of parts of size j (exponent of j in a given partition of n), if m>=1. If m=0 then a(n, 0)=p(n):=A000041(n) (number of partitions of n). O is counted as a part for n=0 and only for this n.
a(n, m) = sum over partitions of n of binomial(q(partition), m), with q the number of distinct parts of a given partition. m>=0.
a(n, m) = a(nm, m1) + a(nm, m), n>=t(m):=m*(m+1)/2=A000217(m) (triangular numbers), else 0, with input a(n, 0) = p(n):=A000041(n).


EXAMPLE

Array begins:
m\n 0 1 2 3 4 .5 .6 .7 .8 ...
0  1 1 2 3 5 .7 11 15 22 ... (A000041)
1  . 1 2 4 7 12 19 ... (A000070)
2  . . . 1 2 .5 .9 ... (A000097)
3  . . . . . .. .1 ... (A000098)
[1]; [1,1]; [2,2]; [3,4,1]; [5,7,2]; [7,12,5]; [11,19,9,1]...
a(3,1) = 4 because the partitions (3), (1,2) and (1^3) have q values 1,2 and 1 which sum to 4.
a(3,1) = 4 because the exponents of part 1 in the above given partitions of 3 are 0,1,3 and they sum to 4.
a(3,1) = 4 because the partitions of 3t(1)=2 with two kinds of part 1, say 1 and 1' and one kind of part 2 are (2),(1^2), (1'^2) and (11').


MAPLE

a:= proc(n, m) option remember; `if`(n<0, 0,
`if`(m=0, combinat[numbpart](n), a(nm, m1) +a(nm, m)))
end:
seq(seq(a(n, m), m=0..round(sqrt(2*n+2))1), n=0..20); # Alois P. Heinz, Nov 16 2012


MATHEMATICA

a[n_, 0] := PartitionsP[n]; a[n_, m_] /; (n >= m*(m+1)/2) := a[n, m] = a[nm, m1] + a[nm, m]; a[n_, m_] = 0; Flatten[ Table[ a[n, m], {n, 0, 18}, {m, 0, Floor[1/2 + Sqrt[2*(n+1)]]  1}]](* JeanFrançois Alcover, May 02 2012, after recurrence formula *)
DeleteCases[Flatten@Transpose@Table[ConstantArray[0, m (m + 1)/2]~Join~Table[Length@IntegerPartitions[n, All, Range@n~Join~Range@m], {n, 0, 21  m (m + 1)/2}] , {m, 0, 6}], 0](* Robert Price, Jul 28 2020 *)


CROSSREFS

The first column (m=0) gives A000041(n). Columns m=1..10 are A000070 (partial sums of partition numbers), A000097, A000098, A000710, A103924A103929.
Sequence in context: A330995 A104567 A087824 * A119473 A002122 A105689
Adjacent sequences: A008948 A008949 A008950 * A008952 A008953 A008954


KEYWORD

nonn,tabf,nice


AUTHOR

N. J. A. Sloane.


EXTENSIONS

More terms from Robert G Bearden (nem636(AT)myrealbox.com), Apr 27 2004
Correction, comments and Riordan formulas from Wolfdieter Lang, Apr 28 2005


STATUS

approved



