A180352 A permutation of Motzkin numbers by reversal of indices in blocks of length 7.

127, 51, 21, 9, 4, 2, 1, 113634, 41835, 15511, 5798, 2188, 835, 323, 142547559, 50852019, 18199284, 6536382, 2356779, 853467, 310572, 208023278209, 73007772802, 25669818476, 9043402501, 3192727797, 1129760415, 400763223

Offset

1,1

Comments

The sequence shows A001006(7) down to A001006(1), then A001006(14) down to A001006(8), etc., varying the index in a sawtooth pattern.

When I initially logged in to use the OEIS, it 'pre-loaded' the search box with a sequence. The seven terms 127,51,21,9,4,2,1 are obtained from that original one by reversing the terms.

"Periodic" term reversals of this sort are routinely encountered when writing out convolution sums.

Links

Table of n, a(n) for n=1..28.

Formula

Let r(n) = 7, 6, 5 ,4, 3, 2, 1 (n>=1), extended with r(n+7)=7+r(n), then a(n) = A001006(r(n)).

Prog

(Sage) A180352 = lambda n: A001006(7*((n-1)//7+1)-((n-1) % 7)) # D. S. McNeil, Dec 06 2010

Crossrefs

Cf. A001006, A073794

Sequence in context: A186995 A145586 A340344 * A217557 A320571 A082456

Adjacent sequences: A180349 A180350 A180351 * A180353 A180354 A180355

Keyword

less,easy,nonn

Author

Matt Insall (insall(AT)mst.edu), Aug 29 2010

Status

approved