A344653 - OEIS

A344653

Every permutation of the prime factors of n has a consecutive monotone triple, i.e., a triple (..., x, y, z, ...) such that either x <= y <= z or x >= y >= z.

8, 16, 24, 27, 32, 40, 48, 54, 56, 64, 80, 81, 88, 96, 104, 112, 125, 128, 135, 136, 144, 152, 160, 162, 176, 184, 189, 192, 208, 224, 232, 240, 243, 248, 250, 256, 270, 272, 288, 296, 297, 304, 320, 324, 328, 336, 343, 344, 351, 352, 368, 375, 376, 378, 384

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OFFSET

1,1

COMMENTS

Differs from A335448 in lacking squares and having 270 etc.

First differs from A345193 in having 270.

Such a permutation is characterized by being neither a twin (x,x) nor wiggly (A025047, A345192). A sequence is wiggly if it is alternately strictly increasing and strictly decreasing, starting with either. For example, the partition (3,2,2,2,1) has no wiggly permutations, even though it has anti-run permutations (2,3,2,1,2) and (2,1,2,3,2).

The Heinz number of a partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k). This gives a bijective correspondence between positive integers and integer partitions.

LINKS

Table of n, a(n) for n=1..55.

FORMULA

Complement of A001248 in A345171.

EXAMPLE

The sequence of terms together with their prime indices begins:

8: {1,1,1}

16: {1,1,1,1}

24: {1,1,1,2}

27: {2,2,2}

32: {1,1,1,1,1}

40: {1,1,1,3}

48: {1,1,1,1,2}

54: {1,2,2,2}

56: {1,1,1,4}

64: {1,1,1,1,1,1}

80: {1,1,1,1,3}

81: {2,2,2,2}

88: {1,1,1,5}

96: {1,1,1,1,1,2}

For example, 36 has prime indices (1,1,2,2), which has the two wiggly permutations (1,2,1,2) and (2,1,2,1), so 36 is not in the sequence.

MATHEMATICA

Select[Range[100], Select[Permutations[Flatten[ConstantArray@@@FactorInteger[#]]], !MatchQ[#, {___, x_, y_, z_, ___}/; x<=y<=z||x>=y>=z]&]=={}&]

CROSSREFS

A superset of A335448, counted by A325535.

Positions of 0's in A344606.

These partitions are counted by A344654.

The complement is A344742, counted by A344740.

The separable case is A345173, counted by A345166.

A000041 counts partitions of 2n with alternating sum 0, ranked by A000290.

A001250 counts wiggly permutations.

A003242 counts anti-run compositions.

A025047 counts wiggly compositions (ascend: A025048, descend: A025049).

A325534 counts separable partitions, ranked by A335433.

A344604 counts wiggly compositions with twins.

A345164 counts wiggly permutations of prime indices.

A345165 counts partitions without a wiggly permutation, ranked by A345171.

A345170 counts partitions with a wiggly permutation, ranked by A345172.

A345192 counts non-wiggly compositions.

Cf. A001222, A071321, A071322, A316523, A316524, A335126, A344614, A344615, A344616, A344652, A345163, A345168, A345193.

Sequence in context: A137845 A046099 A375145 * A345193 A365866 A033859

Adjacent sequences: A344650 A344651 A344652 * A344654 A344655 A344656

KEYWORD

nonn

AUTHOR

Gus Wiseman, Jun 12 2021

STATUS

approved