A376342 - OEIS

A376342

Positions of 1's in the run-compression (A376305) of the first differences (A076259) of the squarefree numbers (A005117).

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 22, 24, 26, 28, 30, 32, 34, 36, 38, 41, 43, 45, 47, 49, 51, 54, 56, 58, 60, 62, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 124, 126, 128, 130

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OFFSET

1,2

COMMENTS

We define the run-compression of a sequence to be the anti-run obtained by reducing each run of repeated parts to a single part. Alternatively, we can remove all parts equal to the part immediately to their left. For example, (1,1,2,2,1) has run-compression (1,2,1).

LINKS

Table of n, a(n) for n=1..62.

EXAMPLE

The sequence of squarefree numbers (A005117) is:

1, 2, 3, 5, 6, 7, 10, 11, 13, 14, 15, 17, 19, 21, 22, 23, 26, 29, 30, ...

with first differences (A076259):

1, 1, 2, 1, 1, 3, 1, 2, 1, 1, 2, 2, 2, 1, 1, 3, 3, 1, 1, 2, 1, 1, 2, 1, ...

with run-compression (A376305):

1, 2, 1, 3, 1, 2, 1, 2, 1, 3, 1, 2, 1, 2, 1, 2, 1, 3, 1, 4, 2, 1, 2, 1, ...

with ones at (A376342):

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 22, 24, 26, 28, 30, 32, 34, 36, 38, ...

MATHEMATICA

Join@@Position[First /@ Split[Differences[Select[Range[100], SquareFreeQ]]], 1]

CROSSREFS

Before compressing we had A076259.

Positions of 1's in A376305.

The version for nonsquarefree numbers gives positions of ones in A376312.

For prime instead of squarefree numbers we have A376343.

A000040 lists the prime numbers, differences A001223.

A000961 and A246655 list prime-powers, differences A057820.

A003242 counts compressed compositions, ranks A333489.

A005117 lists squarefree numbers, differences A076259 (ones A375927).

A013929 lists nonsquarefree numbers, differences A078147.

A116861 counts partitions by compressed sum, by compressed length A116608.

A274174 counts contiguous compositions, ranks A374249.

Cf. A007674, A037201, A053797, A053806, A061398, A072284, A120992, A373198, A376306, A376307, A376308, A376311.

Sequence in context: A378175 A305468 A143452 * A372293 A288452 A338316

Adjacent sequences: A376339 A376340 A376341 * A376343 A376344 A376345

KEYWORD

nonn

AUTHOR

Gus Wiseman, Sep 24 2024

STATUS

approved