OFFSET
1,2
COMMENTS
Are there any unitary abundant numbers (A034683) in this sequence?
a(12) > 10^11.
a(13) > 8*10^12. Also terms: 2^36 * 68719644673, 2^48 * 281474901625261, 2^64 * 18446632096776339457. - Giovanni Resta, May 29 2020
EXAMPLE
MATHEMATICA
usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); udef[n_] := 2*n - usigma[n]; Select[Range[30000], udef[#] == udef[# + 1] &]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, May 28 2020
EXTENSIONS
a(12) from Giovanni Resta, May 29 2020
STATUS
approved