OFFSET
1,1
COMMENTS
Numbers such that d(n)=2*omega(n), where d = A000005 is the number of divisors.
Numbers n such that half of number of divisors of n is equal to number of distinct primes dividing n.
Numbers p*q such that p is 1 or a prime and q is a prime greater than p.
LINKS
Felix Fröhlich, Table of n, a(n) for n = 1..9999
FORMULA
EXAMPLE
a(1)=2 (d(2)=2*omega(2)); a(2)=3 (d(3)=2*omega(3)).
MAPLE
omega := proc(n) if n = 1 then 0 ; else nops( numtheory[factorset](n)) ; end if; end proc: isA167171 := proc(n) numtheory[tau](n) = 2*omega(n) ; end proc: for n from 1 to 300 do if isA167171(n) then printf("%d, ", n) ; end if ; end do: # R. J. Mathar, Oct 31 2009
MATHEMATICA
a = {}; Do[If[1 <= PrimeOmega[n] <= 2 && SquareFreeQ[n], AppendTo[a, n]], {n, 123}]; a (* L. Edson Jeffery, Jan 01 2015 *)
PROG
(PARI) for(n=1, 1e3, if(numdiv(n)==2*omega(n), print1(n, ", "))) \\ Felix Fröhlich, Aug 11 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Oct 29 2009
EXTENSIONS
Corrected by R. J. Mathar, Oct 31 2009
New name from Charles R Greathouse IV, Apr 05 2017
STATUS
approved