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A108113 Numbers k such that the string 3137k is prime. 1

%I

%S 9,11,17,21,27,39,41,63,77,83,117,137,143,159,171,179,201,209,243,257,

%T 263,311,357,371,389,399,447,461,471,507,509,513,521,531,551,567,569,

%U 573,593,609,611,623,627,663,669,681,699,723,731,747,749,777,803,837

%N Numbers k such that the string 3137k is prime.

%C 31 and 37 are primes.

%H Harvey P. Dale, <a href="/A108113/b108113.txt">Table of n, a(n) for n = 1..1000</a>

%e If k=9, then 3137k = 31379 (prime).

%e If k=83, then 3137k = 313783 (prime).

%p a:=proc(n) local z: z:=nops(convert(n,base,10)): if isprime(3137*10^z+n)=true then n else fi end: seq(a(n),n=1..1000); # _Emeric Deutsch_, Jul 02 2005

%t Select[Range[900],PrimeQ[3137*10^IntegerLength[#]+#]&] (* _Harvey P. Dale_, Mar 19 2015 *)

%o (MAGMA) [ n: n in [1..900] | IsPrime(Seqint(Intseq(n) cat [7, 3, 1, 3])) ]; // _Vincenzo Librandi_, Feb 03 2011

%K nonn,base

%O 1,1

%A _Parthasarathy Nambi_, Jun 25 2005

%E More terms from _Emeric Deutsch_, Jul 02 2005

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Last modified January 24 07:15 EST 2020. Contains 331189 sequences. (Running on oeis4.)