OFFSET
1,2
LINKS
Carl R. White, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
90 written in binary is 1011010. There are three 0's in this binary representation. 90 has the prime factorization: 2^1 *3^2 *5^1. There are 3 distinct primes dividing 90. Since the number of 0's in the binary representation equals the number of distinct primes dividing 90, then 90 is in the sequence.
MAPLE
A080791 := proc(n) local dgs ; dgs := convert(n, base, 2) ; nops(dgs)-add(i, i=dgs) ; end: A001221 := proc(n) nops(numtheory[factorset](n)) ; end: isA140707 := proc(n) RETURN( A080791(n) = A001221(n)) ; end: for n from 1 to 300 do if isA140707(n) then printf("%d, ", n) ; fi; od: # R. J. Mathar, Aug 08 2008
MATHEMATICA
Select[Range[300], DigitCount[#, 2, 0]==PrimeNu[#]&] (* Harvey P. Dale, Dec 08 2017 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Leroy Quet, Jul 11 2008
EXTENSIONS
Extended beyond 42 by R. J. Mathar, Aug 08 2008
STATUS
approved