OFFSET
1,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
EXAMPLE
a(1) = 1 since 1 has 1 divisor and 1 binary digit.
a(2), a(3) = 2, 3 since 2 = 10_2 and 3 = 11_2 have 2 divisors and 2 binary digits.
a(4) = 4 = 100_2 is the only number with 3 binary digits having 3 divisors.
8, 10, 14, 15 have 4 binary digits and 4 divisors.
MATHEMATICA
Select[Range[500], DivisorSigma[0, #] == IntegerLength[#, 2] &] (* G. C. Greubel, Nov 08 2016 *)
PROG
(PARI) for(d=1, 10, for(n=2^(d-1), 2^d-1, d==numdiv(n)&print1(n", ")))
(Python)
from sympy import divisor_count
def ok(n): return divisor_count(n) == n.bit_length()
print(list(filter(ok, range(1, 977)))) # Michael S. Branicky, Jul 29 2021
CROSSREFS
KEYWORD
base,nonn
AUTHOR
M. F. Hasler, Nov 28 2007
STATUS
approved