A087247 Squarefree deficient nonprime numbers.

1, 10, 14, 15, 21, 22, 26, 33, 34, 35, 38, 39, 46, 51, 55, 57, 58, 62, 65, 69, 74, 77, 82, 85, 86, 87, 91, 93, 94, 95, 105, 106, 110, 111, 115, 118, 119, 122, 123, 129, 130, 133, 134, 141, 142, 143, 145, 146, 154, 155, 158, 159, 161, 165, 166, 170, 177, 178, 182, 183

Offset: 1

Author

Labos Elemer, Sep 05 2003

Keywords

• nonn

Examples

			105 = 3*5*7 and sigma(105) = 1 + 3 + 5 + 7 + 15 + 21 + 35 + 105 = 192 < 210 = 2*105, so 105 is in the sequence.
The sequence differs from A006881: first term with 3 distinct prime factors is 105.
		

Links

• Enrique Pérez Herrero, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A087244, A087245, A087246, A087248.

Cf. A008683, A000203, A013929, A005117, A005100, A005101.

Programs

Mathematica

isA087247[n_] := SquareFreeQ[n] && !PrimeQ[n] && (DivisorSigma[1, n] < 2n); Select[Range[200], isA087247] (* Enrique Pérez Herrero, Jan 13 2011 *)

PARI

isok(n) = !isprime(n) && issquarefree(n) && (sigma(n) < 2*n); \\ Michel Marcus, Jul 09 2018