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A032692 Exactly 2 digits from {1,2,3,4,5,6,7,8,9} can precede a(n) to form a prime. 1
17, 117, 119, 123, 131, 143, 147, 157, 159, 173, 177, 191, 193, 197, 199, 201, 207, 227, 233, 239, 241, 247, 251, 261, 263, 279, 289, 291, 299, 303, 317, 321, 327, 331, 339, 341, 353, 357, 359, 363, 367, 369, 387, 407, 409, 411, 427, 429, 439, 443, 469 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
If a(n) = 469 then we find '3'469 and '6'469 to be primes.
MATHEMATICA
Select[Range[500], Count[Table[FromDigits[Join[{n}, IntegerDigits[#]]], {n, 9}], _?PrimeQ]==2&] (* Harvey P. Dale, Aug 27 2017 *)
CROSSREFS
Sequence in context: A196643 A196598 A222370 * A293877 A044349 A044730
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, May 15 1998
STATUS
approved

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Last modified May 27 06:20 EDT 2024. Contains 372848 sequences. (Running on oeis4.)