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A032667 Digit '4' concatenated with a(n) is a prime. 2
1, 3, 7, 19, 21, 31, 33, 39, 43, 49, 57, 61, 63, 67, 79, 87, 91, 99, 111, 127, 129, 133, 139, 153, 157, 159, 177, 201, 211, 217, 219, 229, 231, 241, 243, 253, 259, 261, 271, 273, 283, 289, 297, 327, 337, 339, 349, 357, 363, 373, 391, 397, 409 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Obviously there can be no even terms in this sequence. - Alonso del Arte, Jun 18 2017

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..10000 (terms 1..1740 from Vincenzo Librandi)

EXAMPLE

Concatenate 4 and 1 to get 41, which is prime, so 1 is in the sequence.

Concatenate 4 and 3 to get 43, which is prime, so 3 is in the sequence.

Concatenate 4 and 5 to get 45 = 3^2 * 5, which is not prime, so 5 is not in the sequence.

MATHEMATICA

Select[2Range[250] - 1, PrimeQ[FromDigits[Join[{4}, IntegerDigits[#]]]] &] (* Alonso del Arte, Jun 18 2017 *)

PROG

(PARI) isok(n) = isprime(eval(concat(4, Str(n)))); \\ Michel Marcus, Jun 19 2017

CROSSREFS

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).

Sequence in context: A242170 A032675 A089749 * A109991 A248219 A322963

Adjacent sequences:  A032664 A032665 A032666 * A032668 A032669 A032670

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, May 15 1998

EXTENSIONS

Offset adjusted at the suggestion of Michel Marcus by Alonso del Arte, Jun 18 2017

STATUS

approved

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Last modified January 17 20:36 EST 2020. Contains 330987 sequences. (Running on oeis4.)