A306875 Lesser of reduced unitary amicable pair.

172622505, 6217560734, 16017860054, 18102483014, 20021589510, 31285993970, 32576024810, 39270110990, 68700877014, 80170395410, 81142298930, 99542647490, 125182657005, 144194617490, 153113328654, 181335043274, 318710758730, 374642686418, 378482712530, 455440763414

Offset: 1

Author

Amiram Eldar, Mar 14 2019

Keywords

• nonn

Comments

A pair m < n is a reduced unitary amicable pair if usigma(m) = usigma(n) = m + n + 1, where usigma(n) is the sum of unitary divisors of n (A034460).

The larger members are in A306876.

Examples

			172622505 is in the sequence since it is the lesser of the amicable pair (172622505, 175742294): usigma(172622505) = usigma(175742294) = 348364800 = 172622505 + 175742294 + 1.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..28 (terms below 10^12, from David Moews's site).
• David Moews, Perfect, amicable and sociable numbers
• J. O. M. Pedersen, Tables of Aliquot Cycles

Crossrefs

Cf. A003502, A002952, A126172, A034460, A306876.

Programs

Mathematica

us[n_] := Times @@ (1 + Power @@@ FactorInteger[n]) - n;  s={}; Do[m = us[n] - 1; If[m > n && us[m] == n + 1, AppendTo[s, n]], {n, 1, 10^9}]; s