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a(n) is the least number k such that 1/prime(k) has repeating decimal expansion of period n.
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%I #10 Nov 09 2020 21:34:11

%S 1,2,5,12,26,13,4,52,21,28693,1128,2431,1221,16,71954,11,7,153888,8,

%T 27417323062119920,496,14,9,223378173194137397198,5760923,2403,149,

%U 134,10,452,47,406,71,19,27,20,37607875619,150886,22544062111497849

%N a(n) is the least number k such that 1/prime(k) has repeating decimal expansion of period n.

%H <a href="/index/1#1overn">Index entries for sequences related to decimal expansion of 1/n</a>

%F a(0) = 1; a(n) = A000720(A007138(n)).

%e 1/prime(1) = 1/2 = 0.5 (finite decimal expansion).

%e 1/prime(2) = 1/3 = 0.3(3)... (period 1).

%e 1/prime(5) = 1/11 = 0.09(09)... (period 2).

%e 1/prime(12) = 1/37 = 0.027(027)... (period 3).

%Y Cf. A000720, A002371, A003060, A007138.

%K nonn,base

%O 0,2

%A _Ilya Gutkovskiy_, Nov 09 2020

%E a(19)-a(38) from _Daniel Suteu_, Nov 09 2020 [using data from A007138 and A234317]