A075897 1 if binary weight of n is 1 or 2, otherwise 0.

0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 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, 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

Author

Benoit Cloitre, Mar 29 2003

Keywords

• nonn
• easy

Links

• Index entries for characteristic functions

Crossrefs

Cf. A000120, A048645.

Programs

Mathematica

Table[If[MemberQ[{1,2},Total[IntegerDigits[n,2]]],1,0],{n,0,120}] (* Harvey P. Dale, Jul 26 2017 *)

PARI

a(n)=(hammingweight(n)+1)\2 == 1 \\ Charles R Greathouse IV, Jan 10 2022

PARI

a(n)=(hammingweight(n)) <= 2 && n > 0 \\ David A. Corneth, Jan 11 2022

Python

def a(n): return int(bin(n).count('1') in [1, 2])
print([a(n) for n in range(105)]) # Michael S. Branicky, Jan 11 2022

Formula

a(n) = 1 if n is in A048645, 0 otherwise.

For n>0: a(n) = 0^floor(A000120(n)/3). - Reinhard Zumkeller, Apr 07 2003