The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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 A143562 A261425 Adjacent sequences:  A034818 A034819 A034820 * A034822 A034823 A034824 KEYWORD nonn,base AUTHOR Patrick De Geest, Oct 15 1998 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 25 03:53 EDT 2021. Contains 346283 sequences. (Running on oeis4.)