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A088784 Primes formed by concatenating a prime with the preceding prime. 6
53, 5347, 5953, 6761, 137131, 179173, 211199, 223211, 239233, 263257, 359353, 541523, 593587, 613607, 631619, 653647, 659653, 757751, 809797, 977971, 997991, 1009997, 11091103, 11291123, 12371231, 13991381, 15591553, 17831777, 19311913, 19791973, 19931987, 23092297 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

K. D. Bajpai, Table of n, a(n) for n = 1..10300

FORMULA

If isprime(p(n) and p(n-1)) then sequence.add(p(n)& p(n-1)).

EXAMPLE

a(2) = 5347 because 5347 is 53 (a prime) concatenated with 47 (the preceding prime).

MATHEMATICA

concatpr[n_]:=FromDigits[Join[IntegerDigits[n], IntegerDigits[ NextPrime[ n, -1]]]]; Select[concatpr/@Prime[Range[400]], PrimeQ] (* Harvey P. Dale, May 12 2011 *)

PROG

(PARI)

for(n=1, 10^3, p=prime(n); q=concat(Str(p), Str(precprime(p-1))); if(isprime(eval(q)), print1(q, ", "))) \\ Derek Orr, Aug 14 2014

CROSSREFS

Cf. A088712.

Sequence in context: A013542 A200917 A234630 * A104820 A093253 A293080

Adjacent sequences:  A088781 A088782 A088783 * A088785 A088786 A088787

KEYWORD

base,nonn

AUTHOR

Chuck Seggelin (barkeep(AT)plasteredDragon.com), Oct 15 2003

EXTENSIONS

Terms a(30), a(31) and a(32) added by K. D. Bajpai, Aug 14 2014

STATUS

approved

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Last modified June 6 17:33 EDT 2020. Contains 334831 sequences. (Running on oeis4.)