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A069688
Primes that yield another prime on placing a 3 on both sides (as leading and trailing digits).
7
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
OFFSET
1,1
LINKS
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
KEYWORD
nonn,base
AUTHOR
Amarnath Murthy, Apr 06 2002
EXTENSIONS
Edited and extended by Robert G. Wilson v, May 03 2002
STATUS
approved