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A247154 a(n) = smallest composite c such that n^(A000010(c)) == 1 (mod c^2), i.e., smallest composite Wieferich number to base n. 1
4, 3279, 22, 3279, 41542, 330805, 4, 3279, 4, 1461, 142, 1812389, 1726, 3883, 4, 3279, 4, 35, 6, 1967 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(21) > 10^9

a(22)-a(28): 39, 4, 128165, 4, 9, 22, 9

a(29) > 10^9

a(30)-a(33): 1123787, 4, 3279, 4

a(34) > 10^9

LINKS

Table of n, a(n) for n=1..20.

William D. Banks, Florian Luca, Igor E. Shparlinski, Estimates for Wieferich numbers, The Ramanujan Journal, December 2007, Volume 14, Issue 3, pp 361-378.

Takashi Agoh, Karl Dilcher, Ladislav Skula, Fermat Quotients for Composite Moduli, Journal of Number Theory, September 1997, Volume 66, Issue 1, pp 29-50.

PROG

(PARI) for(n=1, 20, forcomposite(c=1, 1e9, if(Mod(n, c^2)^(eulerphi(c))==1, print1(c, ", "); next({2}))); print1("--, "))

CROSSREFS

Cf. A039951, A077816, A241977, A241978, A242958, A242959, A242960, A245529.

Sequence in context: A132639 A132643 A079193 * A134908 A114498 A069120

Adjacent sequences:  A247151 A247152 A247153 * A247155 A247156 A247157

KEYWORD

nonn,more

AUTHOR

Felix Fröhlich, Nov 21 2014

STATUS

approved

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Last modified October 20 07:16 EDT 2021. Contains 348099 sequences. (Running on oeis4.)