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%I #23 Sep 03 2017 08:34:23
%S 1,3,7,19,21,31,33,39,43,49,57,61,63,67,79,87,91,99,111,127,129,133,
%T 139,153,157,159,177,201,211,217,219,229,231,241,243,253,259,261,271,
%U 273,283,289,297,327,337,339,349,357,363,373,391,397,409
%N Digit '4' concatenated with a(n) is a prime.
%C Obviously there can be no even terms in this sequence. - _Alonso del Arte_, Jun 18 2017
%H Seiichi Manyama, <a href="/A032667/b032667.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1740 from Vincenzo Librandi)
%e Concatenate 4 and 1 to get 41, which is prime, so 1 is in the sequence.
%e Concatenate 4 and 3 to get 43, which is prime, so 3 is in the sequence.
%e Concatenate 4 and 5 to get 45 = 3^2 * 5, which is not prime, so 5 is not in the sequence.
%t Select[2Range[250] - 1, PrimeQ[FromDigits[Join[{4}, IntegerDigits[#]]]] &] (* _Alonso del Arte_, Jun 18 2017 *)
%o (PARI) isok(n) = isprime(eval(concat(4, Str(n)))); \\ _Michel Marcus_, Jun 19 2017
%Y Cf. other digit 'd' concatenated with a(n) is prime sequences: A032664 (d = 1), A032665 (d = 2), A032666 (d = 3), A032668 (d = 5), A032669 (d = 6), A032670 (d = 7), A032671 (d = 8), A032672 (d = 9), A000040 (d = 0).
%K nonn,base
%O 1,2
%A _Patrick De Geest_, May 15 1998
%E Offset adjusted at the suggestion of _Michel Marcus_ by _Alonso del Arte_, Jun 18 2017
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