OFFSET
1,1
COMMENTS
The least term that is not divisible by 3 is 73#/5# = Product_{k=4..21} prime(k) = 1357656019974967471687377449. - Amiram Eldar, Aug 15 2024
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
EXAMPLE
99906807 = 3*7*11*13*17*19*103 is a term since it is an odd squarefree number that is not divisible by 5, and sigma(99906807) = 201277440 > 2*99906807.
MATHEMATICA
ta={{0}}; Do[g=n; s=DivisorSigma[1, n]-2*n; If[Greater[s, 0]&&Equal[Abs[MoebiusMu[n]], 1]&& !Equal[Mod[n, 2], 0]&&!Equal[Mod[n, 5], 0], Print[n, PrimeFactorList[n], s]; ta=Append[ta, n]], {n, 10000000, 100000000}]; {ta=Delete[ta, 1], g}
PROG
(PARI) issfab(k) = my(f = factor(k)); issquarefree(f) && sigma(f, -1) > 2;
is(k) = gcd(k, 10) == 1 && issfab(k); \\ Amiram Eldar, Aug 15 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 20 2005
STATUS
approved