A129351 (k+1)-digit primes which can be represented by 10*q+r where q and r are k-digit primes.

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

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: A190731 A348699 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