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A297850
Least common prime factor of the members of n-th amicable pair, or 0 if the two members of the pair are coprime.
1
2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 3, 3, 2, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 2, 3, 2, 3, 2, 3, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 3, 2, 2
OFFSET
1,1
The question whether a(n) = 0 for any n is an open problem.
This is different from A171092 (cf. Chernykh link).
If a(n) = 0, then A001221(A259180(2*n-1)*A259180(2*n)) > 21 (cf. Hagis, 1975).
Sergei Chernykh, Amicable pairs news
Peter Hagis, Jr., On the Number of Prime Factors of a Pair of Relatively Prime Amicable Numbers, Mathematics Magazine, Vol. 48, No. 5 (1975), pp. 263-266.
Wikipedia, Amicable numbers.
FORMULA
a(n) = A297934(A259180(2*n), A259180(2*n-1)).
a(n) = A020639(A061469(n)), if A061469(n) > 1 and 0 otherwise. - Amiram Eldar, Dec 13 2020
CROSSREFS
Sequence in context: A359238 A320011 A068049 * A171092 A141256 A122921
KEYWORD
nonn
AUTHOR
Felix FrÃ¶hlich, Jan 10 2018
EXTENSIONS
Offset corrected and more terms added by Amiram Eldar, Dec 13 2020
STATUS
approved

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Last modified September 20 05:52 EDT 2024. Contains 376020 sequences. (Running on oeis4.)