

A180335


Number of amicable pairs of the form (2^n * pq, 2^n * rs), where p, q, r, and s are distinct odd primes.


2



0, 2, 1, 7, 3, 3, 2, 7, 1, 8, 4, 8, 7, 5, 6, 15, 4, 9, 9, 14, 8, 15, 8, 15
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OFFSET

1,2


COMMENTS

There are only a finite number of such pairs for each n. A180330(n) is the smallest value of 2^n * pq which is part of an amicable pair. The terms in this sequence equal the count of such amicable pairs in Pedersen's table up to n=22, after which the table stops being a complete list of all amicable pairs of the form 2^n * pq. Currently, Pedersen's table lists 4 such amicable pairs for n=23 when there are actually 8 pairs.


LINKS

Table of n, a(n) for n=1..24.
J. M. Pedersen, Regular type (2,2) amicable pairs


EXAMPLE

Eight pairs for n=23, with new ones indicated by *:
(112072375885373577887744, 112072384861110016147456) *
(1268674663237438821892096, 1268674685089131637243904)
(207428765646084356836425728, 207428778650058836339064832) *
(3201546606177940316018966528, 3201546948253280471426793472)
(3246126368411500102994100224, 3246126753752370852634034176)
(30886958374694867104144818176, 30886959839775761339382759424) *
(58230121837690366602703273984, 58230128772645945195748130816)
(1564092755993481057609717907456, 1564092823984266648474085228544) *


CROSSREFS

Cf. A180650, A180651 (the amicable pairs for each n)
Sequence in context: A090699 A214550 A120903 * A257699 A160535 A258235
Adjacent sequences: A180332 A180333 A180334 * A180336 A180337 A180338


KEYWORD

hard,nonn


AUTHOR

T. D. Noe, Sep 25 2010


STATUS

approved



