A178866 Basic Multinomial Coefficients.

1, 1, 1, 3, 1, 10, 1, 15, 15, 10, 1, 105, 35, 21, 1, 280, 210, 105, 56, 35, 28, 1, 1260, 1260, 378, 280, 126, 84, 36, 1, 6300, 3150, 2520, 2100, 1575, 945, 630, 210, 126, 120, 45, 1, 34650, 17325, 15400, 6930, 6930, 5775, 4620, 4620, 990, 462, 330, 165, 55, 1

Offset: 1

Author

Johannes W. Meijer and Manuel Nepveu (Manuel.Nepveu(AT)tno.nl), Jun 21 2010, Jun 24 2010

Keywords

• easy
• nonn
• tabf

Comments

All multinomial coefficients (MC's) are equal, but some are more equal than others. These are the basic multinomial coefficients (BMC's). The ordinary multinomial coefficients can be generated with the basic multinomial coefficients; see A178867.

A number n can be partitioned in A000041(n) different ways. The seven partitions of n=5 are e.g. [5] = [1+4] = [2+3] = [1+1+3] = [1+2+2] = [1+1+1+2] = [1+1+1+1+1]. We observe that the k-th partition of n will consist of a certain number of 1s (i.e., "singles"), a certain number of 2s (i.e., "pairs"), a certain number of 3s (i.e., "triples"), a certain number of 4s (i.e., "4-tuples") and so on. We denote with qt the number of t-tuples in the k-th partition of n. We observe that for the third partition of n=5 there is one pair (q2=1) and one triple (q3=1).

The multinomial coefficients are defined by M3[n,k] = n!/product((t!)^qt*(qt)!, t = 1..n), see Abramowitz and Stegun. For the third partition M3[5,3] = 10, so there are 10 different ways of distributing one pair (B1, B1) and one triple (B2, B2, B2) over five positions.

We define the BMC's as the multinomial coefficients M3[n,k] for which there are no singles (q1=0) in the k-th partition of n for n>=2. Furthermore we define a(1) = 1.

The number of a(n) terms in a triangle row lead to sequence A002865(n) (n>=2). The row sums lead to sequence A000296(n) (n>=2).

Examples

			The first few triangle rows are (P = Pair; T = Triple; 4-T = 4 Tuple; etc..):
n = 1: 1;
n = 2: 1 (1*P);
n = 3: 1 (1*T);
n = 4: 3 (2*P), 1 (1*4-T);
n = 5: 10 (1*P+1*T), 1 (1*5-T);
n = 6: 15 (3*P), 15 (1*4-T+1*P), 10 (2*T), 1 (1*6-T);
n = 7: 105 (1*T+2*P), 35 (1*4-T+1*T), 21 (1*5-T+1*P), 1 (1*7-T);
		

Links

• M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972, Chapter 24, pp. 822-832.
• Kevin Brown, The Collector's Problem
• J. W. Meijer and M. Nepveu, Euler's ship on the Pentagonal Sea, Acta Nova, Volume 4, No.1, December 2008. pp. 176-187.

Crossrefs

Cf. A036040 (version 1), A080575 (version 2) and A178867 (version 3).

Programs

Maple

with(combinat): nmax:=11; A178866(1):=1: T:=1: for n from 1 to nmax do y(n):=numbpart(n): P(n):=sort(partition(n)): k:=0: for r from 1 to y(n) do if P(n)[r,1]>1 then k:=k+1; B(k):=P(n)[r]: fi; od: A002865(n):=k; for k from 1 to A002865(n) do s:=0: j:=1: while sA002865(n))], `>`): for k from 1 to A002865(n) do M3[n,k]:=a[k] od: for k from 1 to A002865(n) do T:=T+1: A178866(T):= M3[n,k]: od: od: seq(A178866(n),n=1..T);

Formula

n = sum(qt*t, t=1..n)

M3[n,k] = n!/product((t!)^qt*(qt)!, t = 1..n)