A357626 - OEIS

A357626

Numbers k such that the reversed k-th composition in standard order has half-alternating sum 0.

0, 11, 15, 37, 38, 45, 46, 53, 54, 55, 59, 137, 138, 140, 153, 154, 156, 167, 169, 170, 171, 172, 179, 191, 201, 202, 204, 205, 206, 213, 214, 229, 230, 231, 235, 243, 247, 251, 255, 529, 530, 532, 536, 561, 562, 564, 568, 583, 587, 593, 594, 595, 596, 600

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OFFSET

1,2

COMMENTS

We define the half-alternating sum of a sequence (A, B, C, D, E, F, G, ...) to be A + B - C - D + E + F - G - ...

The k-th composition in standard order (graded reverse-lexicographic, A066099) is obtained by taking the set of positions of 1's in the reversed binary expansion of k, prepending 0, taking first differences, and reversing again. This gives a bijective correspondence between nonnegative integers and integer compositions.

LINKS

Table of n, a(n) for n=1..54.

Gus Wiseman, Statistics, classes, and transformations of standard compositions

EXAMPLE

The sequence together with the corresponding compositions begins:

0: ()

11: (2,1,1)

15: (1,1,1,1)

37: (3,2,1)

38: (3,1,2)

45: (2,1,2,1)

46: (2,1,1,2)

53: (1,2,2,1)

54: (1,2,1,2)

55: (1,2,1,1,1)

59: (1,1,2,1,1)

MATHEMATICA

stc[n_]:=Differences[Prepend[Join@@Position[Reverse[IntegerDigits[n, 2]], 1], 0]]//Reverse;

halfats[f_]:=Sum[f[[i]]*(-1)^(1+Ceiling[i/2]), {i, Length[f]}];

Select[Range[0, 100], halfats[Reverse[stc[#]]]==0&]

CROSSREFS

See link for sequences related to standard compositions.

The alternating form is A344619.

Positions of zeros in A357622.

The non-reverse version is A357625.

The skew-alternating form is A357628, reverse A357627.

The version for prime indices is A357631.

The version for Heinz numbers of partitions is A357635.

A124754 gives alternating sum of standard compositions, reverse A344618.

A357637 counts partitions by half-alternating sum, skew A357638.

A357641 counts comps w/ half-alt sum 0, partitions A357639, even A357642.

Cf. A001511, A053251, A357136, A357182, A357183, A357184, A357185, A357621, A357623, A357629, A357633.

Sequence in context: A097512 A032490 A068483 * A241679 A219389 A373443

Adjacent sequences: A357623 A357624 A357625 * A357627 A357628 A357629

KEYWORD

nonn

AUTHOR

Gus Wiseman, Oct 08 2022

STATUS

approved