A114780 - OEIS

%I #8 Dec 05 2013 19:57:14

%S 2,3,5,7,711,913,117,0,323,1729,231,437,0,243,1247,1953,759,0,3367,

%T 3471,2173,2279,0,4089,2597,28101,45103,0,2109,18113,43127,40131,0,

%U 1139,22149,34151,37157,0,13167,62173,37179,17181,0,38193,33197,17199,86211

%N Least multiple of 2n-1 ending in prime(n), 0 if no such number exists.

%C If prime(n) has k digits then a(n) == prime(n) (mod 10^k); a(8r+5) = 0 for r > 1.

%e a(5) = 711, ending in 11 = prime(n) and 711 == 0 (mod 9, the fifth odd number).

%o (PARI) a(n) = {if (((n >=8) && ((n-8) % 5 == 0)), return (0)); k = 1; tn = 2*n-1; p = prime(n); tp = 10^length(Str(p)); while ((k*tn) % tp != p, k++); return (k*tn);} \\ _Michel Marcus_, Sep 15 2013

%Y Cf. A114781.

%K base,nonn

%O 1,1

%A _Amarnath Murthy_, Nov 17 2005

%E More terms from _Joshua Zucker_, May 05 2006