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a(1)=1; thereafter a(n) = smallest prime factor of A261570(n).
2

%I #14 Aug 28 2015 11:08:08

%S 1,11,3,11,41,3,239,11,3,11,11,3,11,11,3,11,11,3,71,21557,19,17,31,

%T 181,17,353,19,31,19,29,17,29,11616377,214141,19,5471,17,13883,3,7,

%U 421219193,3,17,7,3,7,101,3,634324033999,13,19,13,83,13,23,13,19,13,19

%N a(1)=1; thereafter a(n) = smallest prime factor of A261570(n).

%H David Broadhurst and Hiroaki Yamanouchi, <a href="/A261411/b261411.txt">Table of n, a(n) for n = 1..99</a> (First 61 terms from Hiroaki Yamanouchi)

%e A261570(11) = 12345678911987654321 = (11)(59)(34631)(43117)(6373)(1999), so a(10) = 11.

%e Note that a(2007) = A261570(2007) is a 21233-digit (probable) prime.

%Y Cf. A261570, A067063, A075023.

%K nonn

%O 1,2

%A _N. J. A. Sloane_, Aug 24 2015, based on _Robert G. Wilson v_'s comment in A261570.

%E a(41)-a(59) from _Hiroaki Yamanouchi_, Aug 24 2015