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 A177920 Numbers k such that k^3 divides 20^(k^2) - 1. 16
 1, 19, 7805561, 1432001198261, 3661225986659, 58130944174609, 187470481770989 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 19 divides a(n) for n > 1. LINKS MATHEMATICA Join[{1}, Select[Range[10000000], PowerMod[20, #^2, #^3] == 1 &]] (* Robert Price, Apr 04 2020 *) CROSSREFS Cf. A128360 (k divides 20^k-1), A128400 (k^2 divides 20^k-1). Cf. A129211, A129212, A177905, A127106, A177907, A127102, A177909, A177243. Cf. A177911, A177912, A177913, A177914, A177915, A177916, A177917, A177918, A177919, A177920. Sequence in context: A013810 A172875 A172839 * A145308 A087515 A038028 Adjacent sequences:  A177917 A177918 A177919 * A177921 A177922 A177923 KEYWORD hard,more,nonn AUTHOR Alexander Adamchuk, May 14 2010 EXTENSIONS a(4)-a(7) from Max Alekseyev, Oct 02 2010 STATUS approved

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Last modified January 22 18:37 EST 2022. Contains 350488 sequences. (Running on oeis4.)