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A089777 a(n) = smallest prime of the form n followed by a prime. 2
13, 23, 37, 43, 53, 67, 73, 83, 97, 103, 113, 127, 137, 1423, 157, 163, 173, 1811, 193, 2011, 2111, 223, 233, 2411, 257, 263, 277, 283, 293, 307, 313, 3217, 337, 347, 353, 367, 373, 383, 397, 4013, 4111, 4211, 433, 443, 457, 463, 4723, 487, 4919, 503, 5113 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Open problem(?): show that a(n) always exists.

LINKS

T. D. Noe, Table of n, a(n) for n=1..10000

MAPLE

cat2 := proc(a, b) local dgs ; dgs := max(1, ilog10(b)+1) ; a*10^dgs+b ; end: A089777 := proc(k) local i, p, q ; for i from 1 do p := ithprime(i) ; q := cat2(k, p) ; if isprime(q) then RETURN(q) ; fi; od: end: for k from 1 to 80 do printf("%d, ", A089777(k)) ; od: # R. J. Mathar, Jan 05 2009

MATHEMATICA

Table[k=2; While[p=FromDigits[Join[IntegerDigits[n], IntegerDigits[Prime[k]]]]; !PrimeQ[p], k++ ]; p, {n, 100}] (* T. D. Noe, Jan 06 2009 *)

CROSSREFS

Cf. A096915 (gives the primes that are appended to n). - R. J. Mathar, Jan 05 2009

Sequence in context: A165459 A108794 A272721 * A050857 A089714 A070219

Adjacent sequences:  A089774 A089775 A089776 * A089778 A089779 A089780

KEYWORD

base,easy,nonn

AUTHOR

Amarnath Murthy, Nov 24 2003

EXTENSIONS

Extended by T. D. Noe and R. J. Mathar, Jan 06 2009

STATUS

approved

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Last modified November 21 17:44 EST 2017. Contains 295004 sequences.