A237978 Number of partitions of n having depth 3; see Comments.

0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 2, 1, 3, 1, 10, 6, 6, 13, 15, 20, 30, 30, 64, 61, 85, 99, 153, 170, 184, 271, 359, 416, 539, 631, 799, 971, 1199, 1433, 1803, 2153, 2692, 3173, 3882, 4544, 5610, 6663, 8090, 9565, 11467, 13590, 16305, 19184, 22933, 26973

Offset: 1

Author

Clark Kimberling, Feb 19 2014

Keywords

• nonn
• easy

Comments

Suppose that P is a partition of n. Let x(1), x(2),...,x(k) be the distinct parts of P, and let m(i) be the multiplicity of x(i) in P. Let f(P) be the partition [m(1)*x(1), m(2)*x(2),...,x(k)*m(k)] of n. Define c(0,P) = P, c(1,P) = f(P),..., c(n,P) = f(c(n-1,P)), and define d(P) = least n such that c(n,P) has no repeated parts; d(P) is introduced here as the depth of P. Clearly d(P) = 0 if and only if P is a strict partition, as in A000009. Conjecture: if d >= 0, then 2^d is the least n that has a partition of depth d.

Examples

			a(14) = 3 counts these partitions: 64211, 632111, 433211.
Successive applications of f to the first of these partitions are indicated by 64211 -> 6422 -> 644 -> 86.
		

Crossrefs

Cf. A237685, A237750, A366063, A000009, A000041.

Programs

Mathematica

z = 60; c[n_] := c[n] = Map[Length[FixedPointList[Sort[Map[Total, Split[#]], Greater] &, #]] - 2 &, IntegerPartitions[n]]
Table[Count[c[n], 1], {n, 1, z}] (* A237685 *)
Table[Count[c[n], 2], {n, 1, z}] (* A237750 *)
Table[Count[c[n], 3], {n, 1, z}] (* this sequence *)
(* Peter J. C. Moses, Feb 19 2014 *)