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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 23 08:18 EDT 2020. Contains 337295 sequences. (Running on oeis4.)