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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

Table of n, a(n) for n=0..47.

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]  [From Harvey P. Dale, Dec. 25, 2010]

CROSSREFS

Cf. A034808-A034821.

Sequence in context: A226698 A096278 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 July 28 00:54 EDT 2021. Contains 346316 sequences. (Running on oeis4.)