OFFSET
1,1
COMMENTS
Odd squarefree numbers n such that sigma(n)/n >= 4/3. - Charles R Greathouse IV, May 30 2014
Includes all odd squarefree multiples of its terms. The primitive members are 3, 35, 715, 935, 1001, 1045, 1105, 1235, 1265, .... - Charles R Greathouse IV, May 30 2014
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
MATHEMATICA
Select[2Range[250] + 1, MoebiusMu[#] != 0 && DivisorSigma[1, #]/# >= 4/3 &] (* Alonso del Arte, May 31 2014 *)
PROG
(PARI) isok(n) = issquarefree(n) && (sumdiv(4*n, d, issquarefree(d)*d) >= 4*n); \\ Michel Marcus, May 30 2014
(PARI) is(n)=my(f=factor(n)); n%2 && n>1 && vecmax(f[, 2])==1 && sigma(f, -1) >= 4/3 \\ Charles R Greathouse IV, May 30 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, May 29 2014
STATUS
approved