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%I #13 Jan 23 2022 20:03:20
%S 1,7,11,17,23,31,43,47,49,53,59,61,67,71,73,77,89,103,113,121,131,133,
%T 139,157,181,191,217,223,239,253,259,269,271,307,323,329,331,341,343,
%U 353,379,397,413,419,421,437,451,463,467,479,491,509,523,547,553,569
%N Numbers k such that the string 1131k is the decimal expansion of a prime number.
%C 11 and 31 are primes.
%C 471 out of the first 1000 terms of this sequence are prime. - _Harvey P. Dale_, Jul 07 2012
%e 11311 is prime, so 1 is a term.
%e 113153 is prime, so 53 is a term.
%t With[{c={1,1,3,1}},Select[Range[600],PrimeQ[FromDigits[ Join[ c,IntegerDigits[ #]]]]&]] (* _Harvey P. Dale_, Jul 07 2012 *)
%o (Magma) [ n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [1, 3, 1, 1])) ];
%Y Cf. A107645, A107644.
%K nonn,base
%O 1,2
%A _Parthasarathy Nambi_, Jun 25 2005
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