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A069688 Primes that yield another prime on placing a 3 on both sides (as leading and trailing digits). 5
5, 7, 31, 37, 41, 43, 53, 59, 61, 67, 73, 79, 83, 101, 103, 139, 151, 157, 179, 197, 223, 241, 257, 263, 269, 271, 283, 293, 307, 311, 349, 353, 389, 421, 431, 461, 467, 491, 557, 593, 599, 601, 607, 631, 643, 647, 683, 691, 701, 727, 757, 769, 811, 827, 839 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..10000

EXAMPLE

139 is a member as 31393 is also a prime.

MATHEMATICA

Select[ Range[1000], PrimeQ[ # ] && PrimeQ[ FromDigits[ Insert[ IntegerDigits[ # ], 3, {{1}, {-1}}]]] &]

Select[Prime[Range[200]], PrimeQ[FromDigits[Join[{3}, IntegerDigits[#], {3}]]]&] (* Harvey P. Dale, Oct 24 2011 *)

CROSSREFS

Cf. A069687, A069689, A069690.

Sequence in context: A307532 A135324 A107639 * A158323 A025119 A025095

Adjacent sequences:  A069685 A069686 A069687 * A069689 A069690 A069691

KEYWORD

nonn,base

AUTHOR

Amarnath Murthy, Apr 06 2002

EXTENSIONS

Edited and extended by Robert G. Wilson v, May 03 2002

STATUS

approved

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Last modified August 8 19:29 EDT 2020. Contains 336298 sequences. (Running on oeis4.)