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A332974
Solutions k of the equation s(k) = s(k-1) + s(k-2) where s(k) = usigma(k) - k is the sum of proper unitary divisors of k (A063919).
1
3, 21, 321, 1257, 3237, 146139, 268713, 584835, 26749089, 9988999095, 25997557299, 54449485353, 935628578283, 2105722150095, 3921293253003, 8234992646643
OFFSET
1,1
COMMENTS
a(17) > 10^13. - Giovanni Resta, May 09 2020
EXAMPLE
21 is a term since s(21) = 11 and s(19) + s(20) = 1 + 10 = 11.
MATHEMATICA
usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); s[n_] := usigma[n] - n; Select[Range[3, 6*10^5], s[#] == s[# - 1] + s[# - 2] &]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Mar 04 2020
EXTENSIONS
a(12)-a(16) from Giovanni Resta, May 09 2020
STATUS
approved