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A319043 Composite numbers k such that Pell(k) == -1 (mod k). 4
741, 3827, 11395, 13067, 27971, 35459, 39059, 84587, 92833, 117739, 134579, 134945, 155819, 177497, 189419, 332949, 382771, 437579, 469699, 473891, 548627, 600059, 632269, 643259, 656083, 677379, 724883, 783579, 828827, 895299, 966779, 1015429, 1021987 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

It appears that most of the terms of A319041 (Numbers k such that Pell(k) == -1 (mod k)) are primes; this sequence lists the composites.

For the composite numbers k such that Pell(k) == 1 (mod k), see A319042.

Numbers that are terms of this sequence seem to be considerably less common than those in A319042; e.g., the numbers of terms in that sequence up to 10^3, 10^4, 10^5, and 10^6 are 5, 21, 67, and 200, respectively, while the corresponding term counts here are only 1, 2, 9, and 31. Why is this?

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..50

EXAMPLE

k=741 is in the sequence: Pell(741) = 741*M - 1 == -1 (mod 741) (where M is a large integer).

k=6 is not in the sequence: Pell(6) = 70 = 6*12 - 2 !== -1 (mod 6).

CROSSREFS

Cf. A000129 (Pell numbers), A094395, A319040, A319041, A319042.

Sequence in context: A243778 A256634 A105391 * A044984 A252576 A188483

Adjacent sequences:  A319040 A319041 A319042 * A319044 A319045 A319046

KEYWORD

nonn

AUTHOR

Jon E. Schoenfield, Sep 08 2018

STATUS

approved

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Last modified August 11 19:26 EDT 2022. Contains 356066 sequences. (Running on oeis4.)