A093812 - OEIS

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.

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

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

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.

LINKS

Table of n, a(n) for n=1..10.

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.

Sequence in context: A091017 A157716 A113968 * A159840 A124609 A102500

Adjacent sequences: A093809 A093810 A093811 * A093813 A093814 A093815

KEYWORD

nonn

AUTHOR

David Wasserman, May 20 2004

STATUS

approved