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Smallest n-digit Carmichael numbers.
1

%I #20 Jun 29 2019 12:32:01

%S 561,1105,10585,101101,1024651,10024561,100427041,1001152801,

%T 10017089857,100023777217,1000151515441,10000879761601,

%U 100000782192961,1000040508690301,10000092861302401,100001371359120001,1000004296444433281,10000011591390633121

%N Smallest n-digit Carmichael numbers.

%e a(4)=1105 because 1105 is the smallest 4-digit Carmichael number. [corrected by _Jon E. Schoenfield_, Jan 28 2014]

%t CarmichaelNbrQ[n_] := ! PrimeQ@ n && Mod[n, CarmichaelLambda@ n] == 1; f[n_] := Block[{k = 10^(n - 1) + 1}, While[! CarmichaelNbrQ@ k, k += 2]; k]; Do[ Print[{n, f[n] // Timing}], {n, 3, 18}]

%Y Cf. A062568, A062852, A063400.

%K hard,more,nonn,base

%O 3,1

%A _Shyam Sunder Gupta_, Feb 17 2002

%E a(17)-a(20) from _Amiram Eldar_, Jun 29 2019