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 A121912 Numbers n such that 10^n == 10 modulo n. 2
 1, 2, 3, 5, 6, 7, 9, 10, 11, 13, 15, 17, 18, 19, 23, 29, 30, 31, 33, 37, 41, 43, 45, 47, 53, 55, 59, 61, 67, 71, 73, 79, 83, 89, 90, 91, 97, 99, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 165, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA By Fermat, all primes are members. EXAMPLE 13 is here because 10^13 = 13*769230769230 + 10. MATHEMATICA Select[Range[250], PowerMod[10, #, # ] == Mod[10, # ] &] (*Chandler*) CROSSREFS Cf. A056969 = 10^n modulo n, A121014. Sequence in context: A285375 A321372 A001948 * A189529 A120514 A101886 Adjacent sequences:  A121909 A121910 A121911 * A121913 A121914 A121915 KEYWORD nonn AUTHOR Zak Seidov, Sep 02 2006 STATUS approved

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Last modified January 23 00:56 EST 2019. Contains 319365 sequences. (Running on oeis4.)