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A151774 Characteristic function of numbers with binary weight 2 (A018900). 5
0, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(A018900(n)) = 1; a(A161989(n)) = 0. - Reinhard Zumkeller, Jun 24 2009

LINKS

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

Index entries for characteristic functions

FORMULA

Let Theta = Sum_{k >= 0} x^(2^k). G.f. is (x + Theta^2 - Theta)/2 (cf. A151758).

MATHEMATICA

w[n_] := IntegerDigits[n, 2] // Total;

a[n_] := Boole[w[n] == 2];

a /@ Range[0, 105] (* Jean-Fran├žois Alcover, Mar 31 2021 *)

PROG

(PARI) a(n)=hammingweight(n)==2 \\ Charles R Greathouse IV, Sep 26 2015

CROSSREFS

Cf. A000120, A018900, A151758.

Sequence in context: A341612 A252742 A066247 * A095792 A288381 A169675

Adjacent sequences:  A151771 A151772 A151773 * A151775 A151776 A151777

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Jun 23 2009

STATUS

approved

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Last modified April 16 07:59 EDT 2021. Contains 343030 sequences. (Running on oeis4.)