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A182665 Greatest x < n such that n divides x*(x-1). 1
0, 1, 1, 1, 1, 4, 1, 1, 1, 6, 1, 9, 1, 8, 10, 1, 1, 10, 1, 16, 15, 12, 1, 16, 1, 14, 1, 21, 1, 25, 1, 1, 22, 18, 21, 28, 1, 20, 27, 25, 1, 36, 1, 33, 36, 24, 1, 33, 1, 26, 34, 40, 1, 28, 45, 49, 39, 30, 1, 45, 1, 32, 36, 1, 40, 55, 1, 52, 46, 56, 1, 64, 1, 38, 51, 57, 56, 66, 1, 65, 1, 42, 1, 64, 51, 44, 58, 56, 1, 81, 78, 69, 63, 48, 76, 64, 1, 50, 55 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

a(n) = 1 iff n is in A246655. - Robert Israel, Jan 13 2015

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

Question on math.stackexchange.com

EXAMPLE

a(6) = 4 because 6 divides 4*3=12 but does not divide 5*4=20.

MAPLE

A:= proc(n)

       max(map(u -> u*modp(1/u, n/u),

                      map(t -> mul(s[1]^s[2], s = t),

                          combinat[powerset](ifactors(n)[2]))))

     end proc;

seq(A(n), n=1..100);

MATHEMATICA

a[n_] := Module[{x}, Max[x /. {ToRules[Reduce[Mod[x*(x-1), n] == 0 && Mod[x*(x+1), n] != 0, x, Integers] /. C[_] -> 0]}]]; a[1] = 0; a[2] = 1; Table[a[n], {n, 1, 100}] (* Jean-Fran├žois Alcover, Mar 04 2014 *)

CROSSREFS

Sequence in context: A306264 A321647 A323410 * A131299 A073937 A074058

Adjacent sequences:  A182662 A182663 A182664 * A182666 A182667 A182668

KEYWORD

nonn,easy

AUTHOR

Robert Israel, Dec 23 2012

STATUS

approved

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Last modified May 19 02:45 EDT 2019. Contains 323377 sequences. (Running on oeis4.)