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A134661 Number of odd coefficients in (1 + x + x^3)^n. 5
1, 3, 3, 7, 3, 9, 7, 13, 3, 9, 9, 19, 7, 21, 13, 27, 3, 9, 9, 21, 9, 27, 19, 35, 7, 21, 21, 41, 13, 39, 27, 55, 3, 9, 9, 21, 9, 27, 21, 39, 9, 27, 27, 55, 19, 57, 35, 73, 7, 21, 21, 49, 21, 63, 41, 75, 13, 39, 39, 79, 27, 81, 55, 109, 3, 9, 9, 21, 9, 27, 21, 39, 9, 27, 27, 57, 21, 63, 39 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Joerg Arndt, Table of n, a(n) for n = 0..10000

S. R. Finch, P. Sebah and Z.-Q. Bai, Odd Entries in Pascal's Trinomial Triangle, arXiv:0802.2654 [math.NT], 2008.

EXAMPLE

From Omar E. Pol, Mar 01 2015: (Start)

Written as an irregular triangle in which the row lengths are the terms of A011782, the sequence begins:

1;

3;

3,7;

3,9,7,13;

3,9,9,19,7,21,13,27;

3,9,9,21,9,27,19,35,7,21,21,41,13,39,27,55;

3,9,9,21,9,27,21,39,9,27,27,55,19,57,35,73,7,21,21,49,21,63,41,75,13,39,39,79,27,81,55,109;

3,9,9,21,9,27,21,39,9,27,27,57,21,63,39...

...

Note that in each row a fraction of the first terms are equal to 3 times the beginning of the sequence itself. For rows 0-6 the fractions are: 0, 1, 1/2, 1/2, 3/8, 3/8, 11/32. Apparently the fractions converge to a constant.

(End)

MATHEMATICA

PolynomialMod[(1+x+x^3)^n, 2] /. x->1

PROG

(PARI) a(n) = {my(pol= Pol([1, 0, 1, 1], xx)*Mod(1, 2)); subst(lift(pol^n), xx, 1); } \\ Michel Marcus, Mar 01 2015

CROSSREFS

Cf. A071053, A038717.

Sequence in context: A145501 A182139 A092693 * A135434 A204204 A164928

Adjacent sequences:  A134658 A134659 A134660 * A134662 A134663 A134664

KEYWORD

nonn

AUTHOR

Steven Finch, Jan 25 2008

STATUS

approved

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Last modified August 24 03:51 EDT 2019. Contains 326260 sequences. (Running on oeis4.)