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A256557 a(n) = A166133(n)^2 - 1. 3
0, 3, 15, 8, 63, 48, 35, 24, 143, 120, 99, 80, 255, 224, 195, 168, 440, 399, 360, 323, 288, 575, 528, 483, 4760, 783, 728, 675, 624, 1520, 1443, 1368, 1295, 1224, 1155, 1088, 1023, 960, 899, 840, 1599, 1680, 1763, 1848, 1935, 2024, 2115, 2208 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Let A166133 = B; A166133 is defined as: After b(1)=1, b(2)=2, and b(3)=4, b(n+1) is the smallest divisor of b(n)^2-1 that has not yet appeared in the sequence.

Since it is conjectured that A166133 is a permutation of the natural numbers, it is therefore conjectured that this sequence is a permutation of all numbers of the form n^2-1.

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A166133(n+1)*A256559(n)

MATHEMATICA

s = {1, 2, 4}; Do[d = Divisors[Last[s]^2 - 1]; i = 1; While[i <= Length[d] && MemberQ[s, d[[i]]], i++]; s = Append[s, d[[i]]], {5000}]; t = Table[s[[k]], {k, 1, 5000}]; #^2 - 1 & /@ t; (* Michael De Vlieger, Apr 02 2015, after Hans Havermann at A166133 *)

CROSSREFS

Cf. A166133, A256559.

Sequence in context: A102531 A135546 A138006 * A145179 A297897 A232076

Adjacent sequences:  A256554 A256555 A256556 * A256558 A256559 A256560

KEYWORD

nonn

AUTHOR

Bob Selcoe, Apr 01 2015

STATUS

approved

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Last modified August 25 10:20 EDT 2019. Contains 326324 sequences. (Running on oeis4.)