A068993 Numbers k such that A062799(k) = 4.

6, 10, 14, 15, 16, 21, 22, 26, 33, 34, 35, 38, 39, 46, 51, 55, 57, 58, 62, 65, 69, 74, 77, 81, 82, 85, 86, 87, 91, 93, 94, 95, 106, 111, 115, 118, 119, 122, 123, 129, 133, 134, 141, 142, 143, 145, 146, 155, 158, 159, 161, 166, 177, 178, 183, 185, 187, 194, 201

Offset: 1

Author

Benoit Cloitre, Apr 06 2002

Keywords

• easy
• nonn

Comments

4*a(n)^2 are the solutions to A048272(x) = -Sum_{d|x} (-1)^d = -9. - Benoit Cloitre, Apr 14 2002

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Union of A006881 and A030514.

Cf. A048272, A062799, A113901.

Programs

Mathematica

f[n_] := DivisorSum[n, PrimeNu[#] &]; Select[Range[201], f[#] == 4 &] (* Amiram Eldar, Jul 25 2020 *)

PARI

for(n=1,100,if(sumdiv(n,d,omega(d))==4,print1(n,",")))

PARI

is(n)=my(f=factor(n)[,2]~); f==[1,1] || f==[4] \\ Charles R Greathouse IV, Oct 15 2015

Formula

A113901(a(n)) = 4. - Reinhard Zumkeller, Mar 13 2011