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A073267 Number of compositions (ordered partitions) of n into exactly two powers of 2. 18
0, 0, 1, 2, 1, 2, 2, 0, 1, 2, 2, 0, 2, 0, 0, 0, 1, 2, 2, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 1, 2, 2, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 2, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Starting with 1 = self-convolution of A036987, the characteristic function of the powers of 2. [Gary W. Adamson, Feb 23 2010]

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000

Sen-Peng Eu, Shu-Chung Liu and Yeong-Nan Yeh, Catalan and Motzkin numbers modulo 4 and 8, Eur. J. Combinat. 29 (2008) 1449-1466.

FORMULA

G.f.: (Sum_{k>=0} x^(2^k) )^2. - Vladeta Jovovic, Mar 28 2005

a(n+1) = A000108(n) mod 4, n>=1 [Theorem 2.3 of Eu et al.]. - R. J. Mathar, Feb 27 2008

a(n) = sum (A209229(k)*A036987(n-k): k = 0..n), convolution of characteristic functions of 2^n and 2^n-1. [Reinhard Zumkeller, Mar 07 2012]

a(n+2) = A000168(n) mod 4. - John M. Campbell, Jul 07 2016

EXAMPLE

For 2 there is only composition {1+1}, for 3 there is {1+2, 2+1}, for 4 {2+2}, for 5 {1+4, 4+1}, for 6 {2+4,4+2}, for 7 none, thus a(2)=1, a(3)=2, a(4)=1, a(5)=2, a(6)=2 and a(7)=0.

MAPLE

f:= proc(n) local d;

d:= convert(convert(n, base, 2), `+`);

if d=2 then 2 elif d=1 then 1 else 0 fi

end proc:

0, 0, seq(f(n), n=2..100); # Robert Israel, Jul 07 2016

MATHEMATICA

Table[Count[Map[{#, n - #} &, Range[0, n]], k_ /; Times @@ Boole@ Map[IntegerQ@ Log2@ # &, k] == 1], {n, 0, 88}] (* Michael De Vlieger, Jul 08 2016 *)

PROG

(Haskell)

a073267 n = sum $ zipWith (*) a209229_list $ reverse $ take n a036987_list

-- Reinhard Zumkeller, Mar 07 2012

(PARI)

N=166; x='x+O('x^N);

v=Vec( 'a0 + sum(k=0, ceil(log(N)/log(2)), x^(2^k) )^2 );

v[1] -= 'a0;  v

/* Joerg Arndt, Oct 21 2012 */

CROSSREFS

The second row of the table A073265. The essentially same sequence 1, 1, 2, 1, 2, 2, 0, 1, ... occurs for first time in A073202 as row 105 (the fix count sequence of A073290). The positions of 1's for n > 1 is given by the characteristic function of A000079, i.e. A036987 with offset 1 instead of 0 and the positions of 2's is given by A018900. Cf. also A023359.

Cf. A036987. [Gary W. Adamson, Feb 23 2010]

Sequence in context: A025075 A175609 A038717 * A159981 A071858 A122864

Adjacent sequences:  A073264 A073265 A073266 * A073268 A073269 A073270

KEYWORD

nonn

AUTHOR

Antti Karttunen, Jun 25 2002

STATUS

approved

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Last modified October 21 21:25 EDT 2021. Contains 348155 sequences. (Running on oeis4.)