A072892 - OEIS

A072892

The 4-cycle of the n => sigma(n)-n process. sigma(n) is the sum of divisors of n. (A000203).

1264460, 1547860, 1727636, 1305184, 1264460

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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

Table of n, a(n) for n=1..5.

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