A151774 Characteristic function of numbers with binary weight 2 (A018900).

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

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-François 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