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A180330 Smallest amicable number of the form 2^n * p * q for which the larger member of the amicable pair has the same form, where p and q are distinct odd primes. 4
2620, 10744, 66928, 2082464, 7677248, 1750776704, 749380864, 7074650624, 25937232896, 161899964416, 3949032574976, 56691934109696, 162222327218176, 5469697508737024, 21547979005558784, 48336727662002176 (list; graph; refs; listen; history; text; internal format)



That is, the amicable pair is (2^n pq, 2^n rs) for odd primes p, q, r, s. See A180331 for the numbers 2^n rs. It is easy to show that the four primes must satisfy the equation (p+1)(q+1) = (r+1)(s+1). These amicable pairs are a subset of the regular type (2,2) pairs, which are cataloged by Pedersen. These amicable pairs can be found by using Herman te Riele's method 2. Amicable pairs of this form are known for 1 < n < 49. Do they exist for all n?


Table of n, a(n) for n=2..17.

J. M. Pedersen, Regular type (2,2) amicable pairs

Herman J. J. te Riele, On generating new amicable pairs from given amicable pairs, Math. Comp. 42 (1984), 219-223.


Sequence in context: A066871 A180650 A245008 * A238921 A156398 A139675

Adjacent sequences:  A180327 A180328 A180329 * A180331 A180332 A180333




T. D. Noe, Sep 07 2010



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Last modified January 18 00:52 EST 2022. Contains 350410 sequences. (Running on oeis4.)