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 A034809 Concatenation of 'n and prevprime(n)' is a prime. 2
 4, 5, 9, 10, 16, 24, 33, 36, 42, 46, 51, 53, 56, 59, 63, 66, 67, 69, 75, 76, 78, 81, 87, 96, 102, 106, 108, 111, 114, 116, 123, 125, 129, 130, 135, 137, 144, 145, 147, 148, 153, 156, 159, 170, 171, 177, 179, 180, 184, 187, 190, 192, 195, 196, 198, 207, 211, 214 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 EXAMPLE n=156 -> previous prime is 151 and '156151' is a prime. MATHEMATICA Select[Range[250], PrimeQ[FromDigits[Join[IntegerDigits[#], IntegerDigits[ NextPrime[ #, -1]]]]]&] (* Harvey P. Dale, Jul 10 2017 *) CROSSREFS Cf. A034808-A034821. Sequence in context: A059582 A257058 A189889 * A096808 A067261 A001161 Adjacent sequences:  A034806 A034807 A034808 * A034810 A034811 A034812 KEYWORD nonn,base AUTHOR Patrick De Geest, Oct 15 1998. STATUS approved

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Last modified January 23 00:56 EST 2019. Contains 319365 sequences. (Running on oeis4.)