A023534 Numbers n such that the largest power of 2 dividing n equals 2^omega(n).

1, 2, 12, 20, 28, 36, 44, 52, 68, 76, 92, 100, 108, 116, 120, 124, 148, 164, 168, 172, 188, 196, 212, 236, 244, 264, 268, 280, 284, 292, 312, 316, 324, 332, 356, 360, 388, 404, 408, 412, 428, 436, 440, 452, 456, 484, 500, 504, 508, 520, 524, 548, 552, 556

Offset

1,2

Comments

That is, numbers such that A001221(n) is equal to A007814(n).

omega(n) = A001221(n) is the number of distinct primes dividing n.

And A007814(n) is the exponent of the highest power of 2 dividing n.

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

Example

omega(12)=2 and 4=2^2 is the largest power of 2 dividing 12, hence 12 is in the sequence.

Mathematica

Select[Range[600], IntegerExponent[#, 2]==PrimeNu[#]&] (* Harvey P. Dale, Jun 26 2011 *)

Prog

(PARI) isok(n) = omega(n) == valuation(n, 2); \\ Michel Marcus, Apr 16 2015
(Python)
from itertools import count, islice
from sympy.ntheory.factor_ import primenu
def A023534_gen(startvalue=1): # generator of terms
    return filter(lambda n:(~n & n-1).bit_length() == primenu(n), count(max(startvalue, 1)))
A023534_list = list(islice(A023534_gen(), 30)) # Chai Wah Wu, Jul 05 2022

Crossrefs

Cf. A039700, A001221 (omega), A007814 (2-adic valuation).

Sequence in context: A137311 A032407 A136725 * A286683 A326238 A226399

Adjacent sequences: A023531 A023532 A023533 * A023535 A023536 A023537

Keyword

nonn

Author

Benoit Cloitre, Sep 04 2002

Status

approved