The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A238057 Primes which are the concatenation of two primes in exactly two ways. 5
 313, 317, 373, 797, 1373, 1913, 1973, 1997, 2113, 2293, 2311, 2347, 2383, 2389, 2953, 2971, 3167, 3313, 3373, 3593, 3673, 3677, 3719, 3733, 3761, 4337, 4397, 5233, 5347, 5953, 6173, 6197, 6737, 7193, 7331, 7433, 7577, 7877, 7919, 7937, 10313, 10337, 10937 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Giovanni Resta, Table of n, a(n) for n = 1..1000 EXAMPLE 313 is in the sequence because 31 and 3 are both primes, and 3 and 13 are both primes, so there are two ways. MATHEMATICA spl[n_] := Block[{d = IntegerDigits@n, c = 0, z}, z = Length@d; Do[ If[ PrimeQ@ FromDigits@ Take[d, k] && d[[k + 1]] > 0 && PrimeQ@ FromDigits@ Take[d, k - z], c++], {k, z - 1}]; c]; Select[ Prime@ Range@1400, spl[#] == 2 &] (* Giovanni Resta, Feb 27 2014 *) PROG (Haskell) a238057 n = a238057_list !! (n-1) a238057_list = filter ((== 2) . length . f) a000040_list where f x = filter (\(us, vs) -> head vs /= '0' && a010051' (read us :: Integer) == 1 && a010051' (read vs :: Integer) == 1) \$ map (flip splitAt \$ show x) [1 .. length (show x) - 1] -- Reinhard Zumkeller, Feb 27 2014 CROSSREFS Cf. A105184, A238056. Cf. A010051, A000040. Sequence in context: A292197 A083972 A045275 * A097023 A159574 A139656 Adjacent sequences: A238054 A238055 A238056 * A238058 A238059 A238060 KEYWORD nonn,base AUTHOR Colin Barker, Feb 17 2014 STATUS approved

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

Last modified May 22 23:49 EDT 2024. Contains 372758 sequences. (Running on oeis4.)