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 A128360 Numbers k such that k divides 20^k - 1. 14
 1, 19, 361, 6859, 130321, 2476099, 47045881, 148305659, 893871739, 2817807521, 4234136149, 10350100679, 16983563041, 53538342899, 80448586831, 196651912901, 322687697779, 815211156289, 1017228515081, 1432001198261, 1528523149789 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 19 divides a(n) for n > 1. All powers of 19 are terms. a(n) = 19^(n-1) for all to n < 8, while a(8) = A128356(8) = 148305659 = 410819*19^2. Prime divisors of a(n) in the order of appearance are {19, 410819, 617311, 1508981, ...}. - Alexander Adamchuk, May 16 2010 LINKS PROG (PARI) is(n)=Mod(20, n)^n==1 \\ Charles R Greathouse IV, Nov 04 2016 CROSSREFS Cf. A001029, A128358, A014960, A014956, A014951, A014949, A014946, A014945, A067945, A128357, A128356, A128400, A177920. Sequence in context: A208031 A171293 A045609 * A001029 A057685 A243399 Adjacent sequences:  A128357 A128358 A128359 * A128361 A128362 A128363 KEYWORD nonn AUTHOR Alexander Adamchuk, Mar 02 2007 EXTENSIONS a(9)-a(11) from Stefan Steinerberger, May 09 2007 a(12)-a(15) from Alexander Adamchuk, May 16 2010 Edited and a(16)-a(21) added by Max Alekseyev, Oct 02 2010 STATUS approved

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Last modified May 25 19:19 EDT 2022. Contains 354071 sequences. (Running on oeis4.)