OFFSET
1,6
COMMENTS
a(n) = 0 if and only if P(n) is multiperfect. In particular, a(n) = 0 if M(n) is prime.
EXAMPLE
a(6) = 2 since P(6) = 2016 and sigma_{-1}(2016) = 13/2^2.
MATHEMATICA
M[n_] := 2^n - 1;
P[n_] := 2^(n - 1) M[n];
A[n_] := Log[2, Denominator[DivisorSigma[-1, P[n]]]];
PROG
(PARI) a(n) = logint(denominator(sigma(2^(n-1)*(2^n-1), -1)), 2); \\ Michel Marcus, Apr 02 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
David Terr, Apr 02 2019
EXTENSIONS
More terms from Felix Fröhlich, Sep 29 2019
STATUS
approved