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 A015951 Numbers k such that k | 5^k + 1. 24
 1, 2, 3, 9, 21, 26, 27, 63, 81, 147, 189, 243, 338, 441, 567, 609, 729, 903, 1029, 1323, 1378, 1701, 1827, 2187, 2667, 2709, 3087, 3969, 4263, 4394, 4401, 5103, 5481, 6321, 6561, 7203, 8001, 8127, 9261, 9429, 11907, 12789, 13149, 13203 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Jinyuan Wang, Table of n, a(n) for n = 1..5000 (first 500 terms from Seiichi Manyama) MATHEMATICA Select[Range@ 14000, Divisible[5^# + 1, #] &] (* Michael De Vlieger, Oct 10 2016 *) PROG (PARI) isok(n) = Mod(5, n)^n == -1; \\ Michel Marcus, Oct 11 2016 (MAGMA) [n: n in [1..10^5] | Modexp(5, n, n)+1 eq n]; // Jinyuan Wang, Dec 29 2018 (Python) for n in range(1, 10**5):     if pow(5, n, n)+1 == n: print(n, end=', ') # Stefano Spezia, Dec 30 2018 CROSSREFS 5^k+m is divisible by k: A123062 (m=2), A123052 (m=3), A123047 (m=4). Column k=5 of A333429. Sequence in context: A036673 A111189 A001004 * A244666 A101531 A099607 Adjacent sequences:  A015948 A015949 A015950 * A015952 A015953 A015954 KEYWORD nonn AUTHOR STATUS approved

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Last modified April 11 12:00 EDT 2021. Contains 342886 sequences. (Running on oeis4.)