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A129351 (k+1)-digit primes which can be represented by 10*q+r where q and r are k-digit primes. 0
23, 37, 53, 73, 127, 139, 149, 151, 157, 163, 167, 173, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 241, 251, 257, 263, 269, 271, 277, 283, 307, 313, 331, 337, 347, 349, 353, 373, 379, 383, 389, 401, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 487, 491, 499 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

There may be more than one representation of that kind,

for example 2791 = 10*233+461 = 10*239+401 = 10*268+101 = 10*227+521 = 10*251+281 splits the 4-digit prime 2791 into two 3-digit primes in 5 different ways; only one instance (only one 2791 in the example) is added to the sequence then.

LINKS

Table of n, a(n) for n=1..55.

EXAMPLE

a(1)=23 = 10*2+3. a(3)= 53 = 10*5+3. a(5)= 127 = 11*10+17. 167= 10*13+37.

MAPLE

A055642 := proc(n) max(1, ilog10(n)+1) ; end:

isA129351 := proc(p) local np1, q, r ; if isprime(p) then np1 := A055642(p)-1 ; q := nextprime(10^(np1-1)) ; while q < 10^np1 do r := q ; while r < 10^np1 do if 10*q+r = p or 10*r+q = p then return true; end if ; r := nextprime(r) ; end do ; q := nextprime(q) ; end do ; false ; else false; end if; end proc:

for n from 5 to 400 do p := ithprime(n) ; if isA129351(p) then printf("%d, ", p) ; fi; od: # R. J. Mathar, Nov 02 2009

CROSSREFS

Sequence in context: A163759 A190731 A092622 * A179910 A124888 A141521

Adjacent sequences:  A129348 A129349 A129350 * A129352 A129353 A129354

KEYWORD

nonn,easy,base

AUTHOR

J. M. Bergot, May 28 2007

EXTENSIONS

Edited, 139 inserted and sequence extended - R. J. Mathar, Nov 02 2009

STATUS

approved

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Last modified January 19 20:16 EST 2019. Contains 319310 sequences. (Running on oeis4.)