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A128401
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Numbers n such that n^2 divides 21^n-1.
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14
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1, 2, 4, 5, 10, 20, 22, 44, 52, 68, 110, 220, 260, 340, 506, 572, 748, 820, 884, 1012, 2530, 2756, 2860, 3740, 3916, 4108, 4420, 5060, 9020, 9724, 10660, 13156, 13780, 13940, 17204, 19580, 20540, 23782, 29084, 30316, 34060, 45188, 46852, 47564
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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MATHEMATICA
| Select[Range[50000], Divisible[21^#-1, #^2]&] (* From Harvey P. Dale, June 17 2011 *)
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CROSSREFS
| Cf. A127103, A127104, A127105, A127106, A127107, A127102, A127101, A127100, A127092, A128405, A128393, A128394, A128395, A128396, A128397, A128398, A128399, A128400, A128402, A128403, A128404.
Sequence in context: A005018 A118551 A161706 * A018467 A035524 A018283
Adjacent sequences: A128398 A128399 A128400 * A128402 A128403 A128404
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KEYWORD
| nonn,less
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Mar 01 2007
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