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A292392 Numbers n such that n^2 divides (17^n + 1). 1
1, 3, 9, 21, 39, 63, 117, 273, 819, 2067, 3081, 6201, 9243, 12807, 14469, 21567, 43407, 48711, 50877, 64701, 89649, 146133, 149331, 163293, 166491, 221169, 340977, 356139, 447993, 489879, 546819, 661401, 663507, 1022931, 1143051, 1165437, 1548183, 1639911, 1640457 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

After a(1), all the terms are multiples of 3.

From Robert Israel, Sep 18 2017: (Start)

All terms are odd.

If m and n are terms then lcm(m,n) is a term.

If n is a term not divisible by 9, then 3n is a term. (End)

LINKS

Table of n, a(n) for n=1..39.

EXAMPLE

3 appears is a term because 3^2 divides (17^3 + 1): 4914/9 = 546.

9 appears is a term because 9^2 divides (17^9 + 1): 118587876498/81 = 1464047858.

MAPLE

A292392:= proc(n) if(17 &^ n+1)mod (n^2)=0  then RETURN (n); fi; end: seq(A292392(n), n=1..50000);

MATHEMATICA

Select[Range[50000], IntegerQ[(PowerMod[17, #, #^2] + 1)/#^2] &]

PROG

(PARI) for(n=1, 5e6, if (Mod(17, n^2)^n==-1, print1(n, ", ")));

(PARI) is(n) = Mod(17, n^2)^n==-1 \\ Felix Fröhlich, Sep 16 2017

CROSSREFS

Cf. A015951, A123047, A123052, A177813, A292331.

Sequence in context: A259711 A014857 A177817 * A112039 A007518 A029494

Adjacent sequences:  A292389 A292390 A292391 * A292393 A292394 A292395

KEYWORD

nonn

AUTHOR

K. D. Bajpai, Sep 15 2017

STATUS

approved

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Last modified November 13 08:18 EST 2019. Contains 329093 sequences. (Running on oeis4.)