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 A195201 a(n) is the largest prime factor of the number made by taking the previous term and duplicating the final digit, a(1) = 1. 0

%I #20 Aug 27 2015 10:43:47

%S 1,11,37,29,23,233,2333,23333,661,601,6011,6679,997,907,313,241,2411,

%T 47,53,41,137,17,59,599,857,953,9533,13619,19457,821,23,233,2333,

%U 23333,661,601,6011,6679,997,907,313,241,2411,47,53,41,137,17,59,599,857,953

%N a(n) is the largest prime factor of the number made by taking the previous term and duplicating the final digit, a(1) = 1.

%C This sequence is periodic with period (23, 233, 2333, 23333, 661, 601, 6011, 6679, 997, 907, 313, 241, 2411, 47, 53, 41, 137, 17, 59, 599, 857, 953, 9533, 13619, 19457, 821) of length 26.

%H <a href="/index/Rec#order_26">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1).

%e Next term after 11 is 37 because 111 = 3*37. Next term after 37 is 29 because 377 = 13*29. Next term after 821 is 23 because 8211 = 3*7*17*23.

%t NestList[FactorInteger[10#+Mod[#,10]][[-1,1]]&,11,60](* Zak Seidov, Sep 16 2011*)

%K nonn,base,easy

%O 1,2

%A _J. Lowell_, Sep 12 2011

%E a(1) prepended by _Zak Seidov_, Sep 18 2011

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Last modified September 25 05:35 EDT 2023. Contains 365582 sequences. (Running on oeis4.)