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 A034815 Concatenations C1 and C2 are both prime (see the comment lines). 0
 33, 51, 53, 63, 111, 123, 129, 211, 237, 273, 357, 489, 519, 573, 597, 609, 639, 651, 653, 657, 669, 681, 687, 747, 753, 819, 831, 873, 891, 987, 997, 1071, 1611, 1881, 2037, 2049, 2247, 2271, 2613, 2763, 3063, 3267, 3393, 3573, 3969, 4251, 4263, 4293 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS C1 = 'nextprime(n) followed by n' C2 = 'n followed by prevprime(n)' LINKS EXAMPLE n=1881 -> next prime is 1889, previous prime is 1879, thus '18891881' and '18811879' are both primes. MATHEMATICA okQ[n_]:=Module[{idn=IntegerDigits[n], ida, idb}, ida=IntegerDigits[NextPrime[n, -1]]; idb=IntegerDigits[NextPrime[n]]; PrimeQ[FromDigits[Join[idn, ida]]]&&PrimeQ[FromDigits[Join[idb, idn]]]] Select[Range[5000], okQ] (* Harvey P. Dale, Dec 25 2010 *) CROSSREFS Cf. A034808-A034821. Sequence in context: A096278 A349551 A204381 * A014976 A109407 A204374 Adjacent sequences: A034812 A034813 A034814 * A034816 A034817 A034818 KEYWORD nonn,base AUTHOR Patrick De Geest, Oct 15 1998 STATUS approved

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Last modified March 20 05:18 EDT 2023. Contains 361358 sequences. (Running on oeis4.)