OFFSET
1,2
COMMENTS
The first missing integer is 432 (see in A069781).
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..10000
Tanya Khovanova, Non Recursions
EXAMPLE
Below 100000 only 314 integers are missing, collected in A069781.
MATHEMATICA
f[x_] := GCD[DivisorSigma[0, x^3], DivisorSigma[0, x]]; Do[s=f[n]; If[IntegerQ[Log[2, s]], Print[{n, s}]], {n, 1, 100000}]
PROG
(PARI) is(n)=my(f=factor(n)[, 2], g=gcd(prod(i=1, #f, 3*f[i]+1), prod(i=1, #f, f[i]+1))); g>>valuation(g, 2)==1 \\ Charles R Greathouse IV, Oct 16 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Apr 08 2002
STATUS
approved