The On-Line Encyclopedia of Integer Sequences (OEIS)

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A093812

a(1) = 1; for n > 1, a(n) is the smallest positive integer not already used such that a(n)*a(n-1) + 1 is a fourth power.
(history; published version)

#3 by Russ Cox at Sat Mar 31 13:20:56 EDT 2012

AUTHOR

_David Wasserman (wasserma(AT)spawar.navy.mil), _, May 20 2004

Discussion

Sat Mar 31

13:20

OEIS Server: https://oeis.org/edit/global/880

#2 by N. J. A. Sloane at Fri Feb 27 03:00:00 EST 2009

EXAMPLE

The 4th roots of unity mod 17 are 1, 4, 13, and 16. (4^4 - 1)/17 = 15, which has already been used, so 17 is followed by (13^4 - 1)/17 = 1680.

KEYWORD

nonn,new

nonn

#1 by N. J. A. Sloane at Sat Jun 12 03:00:00 EDT 2004

NAME

a(1) = 1; for n > 1, a(n) is the smallest positive integer not already used such that a(n)*a(n-1) + 1 is a fourth power.

DATA

1, 15, 17, 1680, 421, 56086995, 9940915081637, 31271643639794562523698024915, 3090319883395626207270178075850946683940891639487741952, 9721376888636052447184767296534734059409700304429485542107645657085305

OFFSET

1,2

COMMENTS

The next terms are (to two significant digits) 9.6*10^95, 3.0*10^111, 3.0*10^137, 9.4*10^152, 9.3*10^178.

EXAMPLE

The 4th roots of unity mod 17 are 1, 4, 13, and 16. (4^4 - 1)/17 = 15, which has already been used, so 17 is followed by (13^4 - 1)/17 = 1680.

CROSSREFS

Cf. A091569, A083203.

KEYWORD

nonn

AUTHOR

David Wasserman (wasserma(AT)spawar.navy.mil), May 20 2004

STATUS

approved