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%I #14 Jan 17 2019 13:44:08
%S 2,3,4,6,9,10,12,14,18,19,23,24,36,38,39,46,48,62,78,93,96,106,120,
%T 134,150,186,196,240,268,294,300,317,320
%N Values n such that the largest prime factor of repunit R_n=(10^n -1)/9 is a unique prime,i.e.,whose reciprocal has unique decimal period length.
%H M. Kamada, <a href="https://stdkmd.net/nrr/repunit/">Factorization of 11...11(Repunits)</a>
%e 18 is in the sequence because R_18=3^2*7*11*13*19*37*52579*333667 and 333667 is the only prime with period 9: 1/333667 =0.000002997000002997...
%Y Cf. A002275, A003020, A007498, A040017.
%K more,nonn,base
%O 1,1
%A _Lekraj Beedassy_, Jun 18 2006
%E Corrected and extended by _Hans Havermann_, Jun 22 2006
%E a(25)-a(33) from _Ray Chandler_, May 09 2017
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