A279687 - OEIS

A279687

a(0) = 1, a(n) is the least prime factor of a(n-1)^2+1 that has not previously appeared in the sequence for n > 0.

1, 2, 5, 13, 17, 29, 421, 401, 37, 1877, 41

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OFFSET

0,2

LINKS

Table of n, a(n) for n=0..10.

EXAMPLE

a(7) is a prime factor of a(6)^2+1 = 421^2 + 1 = 177242, which factors as 2*13*17*401. 2, 13, and 17 have already appeared in the sequence, so a(7) = 401.

a(10)^2+1 = 882 = 2 * 29^2. Both 2 and 29 have already appeared in the sequence, so it terminates.

CROSSREFS

Cf. A031439.

Sequence in context: A160215 A068486 A099332 * A031439 A087952 A124255

Adjacent sequences: A279684 A279685 A279686 * A279688 A279689 A279690

KEYWORD

nonn,fini,full

AUTHOR

Franklin T. Adams-Watters, Dec 17 2016

STATUS

approved