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A069689 Primes that yield another prime on placing a 7 on both sides (as leading and trailing digits). 7
2, 5, 17, 23, 29, 41, 47, 53, 71, 131, 191, 227, 233, 257, 281, 293, 347, 359, 389, 401, 419, 431, 479, 503, 521, 557, 593, 599, 653, 659, 677, 683, 701, 761, 797, 827, 857, 887, 953, 977, 1091, 1097, 1109, 1151, 1181, 1187, 1193, 1223, 1283, 1307, 1373 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
233 is a member as 72337 is also a prime.
MATHEMATICA
Select[ Range[2000], PrimeQ[ # ] && PrimeQ[ FromDigits[ Insert[ IntegerDigits[ # ], 7, {{1}, {-1}}]]] &]
Select[Prime[Range[250]], PrimeQ[FromDigits[Join[{7}, IntegerDigits[ #], {7}]]]&] (* Harvey P. Dale, Nov 01 2011 *)
CROSSREFS
Sequence in context: A041283 A042049 A341017 * A307479 A106021 A032605
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 February 24 17:27 EST 2024. Contains 370307 sequences. (Running on oeis4.)