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A309019 Expansion of x * Product_{k>=0} (1 + x^(2^k) + x^(2^(k+1)) + x^(2^(k+2))). 3
0, 1, 1, 2, 1, 4, 2, 4, 1, 7, 4, 7, 2, 10, 4, 7, 1, 12, 7, 12, 4, 18, 7, 13, 2, 19, 10, 16, 4, 21, 7, 12, 1, 20, 12, 20, 7, 31, 12, 23, 4, 34, 18, 29, 7, 38, 13, 22, 2, 34, 19, 31, 10, 45, 16, 30, 4, 41, 21, 32, 7, 40, 12, 20, 1, 33, 20, 33, 12, 52, 20, 39, 7, 58, 31, 50, 12, 66, 23, 39, 4, 61, 34, 56, 18, 81, 29, 54, 7, 74, 38 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..90.

FORMULA

a(0) = 0, a(1) = 1; a(2*n) = a(n), a(2*n+1) = a(n-1) + a(n) + a(n+1).

MATHEMATICA

nmax = 90; CoefficientList[Series[x Product[(1 + x^(2^k) + x^(2^(k + 1)) + x^(2^(k + 2))), {k, 0, Floor[Log[2, nmax]] + 1}], {x, 0, nmax}], x]

a[0] = 0; a[1] = 1; a[n_] := If[EvenQ[n], a[n/2], a[(n - 3)/2] + a[(n - 1)/2] + a[(n + 1)/2]]; Table[a[n], {n, 0, 90}]

CROSSREFS

Cf. A002487, A309020, A309021, A309022.

Sequence in context: A274455 A153279 A278425 * A082908 A086449 A321088

Adjacent sequences:  A309016 A309017 A309018 * A309020 A309021 A309022

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, Jul 06 2019

STATUS

approved

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Last modified June 24 14:13 EDT 2021. Contains 345417 sequences. (Running on oeis4.)