A325457 - OEIS

A325457

Heinz numbers of integer partitions with strictly decreasing differences.

1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 13, 14, 15, 17, 18, 19, 21, 22, 23, 25, 26, 29, 31, 33, 34, 35, 37, 38, 39, 41, 43, 46, 47, 49, 50, 51, 53, 55, 57, 58, 59, 61, 62, 65, 67, 69, 70, 71, 73, 74, 75, 77, 79, 82, 83, 85, 86, 87, 89, 91, 93, 94, 95, 97, 98

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OFFSET

1,2

COMMENTS

The Heinz number of an integer partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k).

The differences of a sequence are defined as if the sequence were increasing, so for example the differences of (6,3,1) are (-3,-2).

The enumeration of these partitions by sum is given by A320470.

LINKS

Table of n, a(n) for n=1..65.

Gus Wiseman, Sequences counting and ranking integer partitions by the differences of their successive parts.

EXAMPLE

The sequence of terms together with their prime indices begins:

1: {}

2: {1}

3: {2}

4: {1,1}

5: {3}

6: {1,2}

7: {4}

9: {2,2}

10: {1,3}

11: {5}

12: {1,1,2}

13: {6}

14: {1,4}

15: {2,3}

17: {7}

19: {8}

20: {1,1,3}

21: {2,4}

22: {1,5}

23: {9}

MATHEMATICA

primeptn[n_]:=If[n==1, {}, Reverse[Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]]];

Select[Range[100], Greater@@Differences[primeptn[#]]&]

CROSSREFS

Cf. A056239, A112798, A320470, A320510, A325328, A325352, A325360, A325361, A325368, A325399, A325456, A325461, A320470, A325396.

Sequence in context: A340682 A166155 A342525 * A063538 A167207 A037143

Adjacent sequences: A325454 A325455 A325456 * A325458 A325459 A325460

KEYWORD

nonn

AUTHOR

Gus Wiseman, May 03 2019

STATUS

approved