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A325328 Heinz numbers of finite arithmetic progressions (integer partitions with equal differences). 20
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 19, 21, 22, 23, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 41, 43, 46, 47, 49, 51, 53, 55, 57, 58, 59, 61, 62, 64, 65, 67, 69, 71, 73, 74, 77, 79, 81, 82, 83, 85, 86, 87, 89, 91, 93, 94, 95, 97 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

The enumeration of these partitions by sum is given by A049988.

LINKS

Table of n, a(n) for n=1..67.

Wikipedia, Arithmetic progression.

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

EXAMPLE

Most small numbers are in the sequence. However the sequence of non-terms together with their prime indices begins:

   12: {1,1,2}

   18: {1,2,2}

   20: {1,1,3}

   24: {1,1,1,2}

   28: {1,1,4}

   36: {1,1,2,2}

   40: {1,1,1,3}

   42: {1,2,4}

   44: {1,1,5}

   45: {2,2,3}

   48: {1,1,1,1,2}

   50: {1,3,3}

   52: {1,1,6}

   54: {1,2,2,2}

   56: {1,1,1,4}

   60: {1,1,2,3}

   63: {2,2,4}

   66: {1,2,5}

   68: {1,1,7}

   70: {1,3,4}

For example, 60 is the Heinz number of (3,2,1,1), which has differences (-1,-1,0), which are not equal, so 60 does not belong to the sequence.

MATHEMATICA

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

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

CROSSREFS

Cf. A000961, A007862, A049988, A056239, A112798, A130091, A240026, A289509, A307824, A325327, A325352, A325368, A325405, A325407.

Sequence in context: A236510 A317710 A303554 * A316521 A085156 A102466

Adjacent sequences:  A325325 A325326 A325327 * A325329 A325330 A325331

KEYWORD

nonn

AUTHOR

Gus Wiseman, Apr 23 2019

STATUS

approved

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Last modified February 28 23:19 EST 2020. Contains 332353 sequences. (Running on oeis4.)