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A335550 Number of minimal normal patterns avoided by the prime indices of n in increasing or decreasing order, counting multiplicity. 6
1, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 3, 3, 3, 3, 4, 3, 4, 3, 3, 3, 4, 3, 3, 3, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 3, 3, 4, 4, 3, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 3, 3, 4, 3, 3, 4, 3, 3, 3, 3, 4, 3, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

We define a (normal) pattern to be a finite sequence covering an initial interval of positive integers. Patterns are counted by A000670 and ranked by A333217. A sequence S is said to match a pattern P if there is a not necessarily contiguous subsequence of S whose parts have the same relative order as P. For example, (3,1,1,3) matches (1,1,2), (2,1,1), and (2,1,2), but avoids (1,2,1), (1,2,2), and (2,2,1).

LINKS

Table of n, a(n) for n=1..70.

Wikipedia, Permutation pattern

Gus Wiseman, Sequences counting and ranking compositions by the patterns they match or avoid.

FORMULA

It appears that for n > 1, a(n) = 3 if n is a power of a squarefree number (A072774), and a(n) = 4 otherwise.

EXAMPLE

The a(12) = 4 minimal patterns avoiding (1,1,2) are: (2,1), (1,1,1), (1,2,2), (1,2,3).

The a(30) = 3 minimal patterns avoiding (1,2,3) are: (1,1), (2,1), (1,2,3,4).

CROSSREFS

The version for standard compositions is A335465.

Patterns are counted by A000670.

Sum of prime indices is A056239.

Each number's prime indices are given in the rows of A112798.

Patterns are ranked by A333217.

Patterns matched by compositions are counted by A335456.

Patterns matched by prime indices are counted by A335549.

Patterns matched by partitions are counted by A335837.

Cf. A124770, A124771, A181796, A269134, A299702, A333257, A335452, A335516.

Sequence in context: A087717 A053444 A175797 * A243129 A135717 A335465

Adjacent sequences:  A335544 A335548 A335549 * A335552 A335553 A335554

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Jun 26 2020

STATUS

approved

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Last modified August 12 16:17 EDT 2020. Contains 336439 sequences. (Running on oeis4.)