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A072892
The 4-cycle of the n => sigma(n)-n process. sigma(n) is the sum of divisors of n. (A000203).
4
1264460, 1547860, 1727636, 1305184, 1264460
OFFSET
1,1
COMMENTS
The two smallest members of sociable quadruples (1264460 and 2115324, see A090615) were found by the Canadian mathematician and educator Kenneth Dudley Fryer (1924-1984) in 1965 (Honsberger, 1970). These were the first aliquot cycles of length greater than 2 that were found since 1918 (see A072890 and A072891). They were rediscovered by Cohen (1970). - Amiram Eldar, Mar 24 2024
REFERENCES
Ross Honsberger, Ingenuity in Mathematics, Mathematical Association of America, 1970.
LINKS
Henri Cohen, On amicable and sociable numbers, Math. Comp., Vol. 24, No. 110 (1970), pp. 423-429.
Eric Weisstein's World of Mathematics, Sociable Numbers.
Wikipedia, Sociable number.
FORMULA
a(4+n) = a(n).
MATHEMATICA
NestWhileList[DivisorSigma[1, #] - # &, 1264460, UnsameQ, All] (* Amiram Eldar, Mar 24 2024 *)
CROSSREFS
KEYWORD
fini,full,nonn
AUTHOR
Miklos Kristof, Jul 29 2002
STATUS
approved