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A034821 Concatenations C1 and C2 are both prime (see the comment lines). 13
5, 17, 103, 127, 157, 191, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 227, 234, 235, 236, 237, 238, 258, 259, 260, 261, 262, 307, 347, 354, 355, 356, 357, 358, 431, 524, 525, 526, 527, 528, 529, 530, 531, 532, 533, 534, 535, 536, 537, 538, 539 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

C1 = 'prevprime(n) followed by nextprime(n)'

C2 = 'nextprime(n) followed by prevprime(n)'

LINKS

Table of n, a(n) for n=0..51.

EXAMPLE

n=17 -> next prime is 19, previous prime is 13, thus '1319' and '1913' are both primes.

MATHEMATICA

c1c2pQ[n_]:=Module[{c1=NextPrime[n, -1], c2=NextPrime[n]}, AllTrue[ {c1* 10^IntegerLength[ c2]+c2, c2*10^IntegerLength[c1]+c1}, PrimeQ]]; Select[ Range[600], c1c2pQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 23 2019 *)

CROSSREFS

Cf. A034808-A034820.

Sequence in context: A076516 A145986 A200992 * A158007 A349011 A143562

Adjacent sequences:  A034818 A034819 A034820 * A034822 A034823 A034824

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, Oct 15 1998

STATUS

approved

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Last modified September 28 20:34 EDT 2022. Contains 357081 sequences. (Running on oeis4.)