A106582 Numbers which are the concatenation of two primes.

22, 23, 25, 27, 32, 33, 35, 37, 52, 53, 55, 57, 72, 73, 75, 77, 112, 113, 115, 117, 132, 133, 135, 137, 172, 173, 175, 177, 192, 193, 195, 197, 211, 213, 217, 219, 223, 229, 231, 232, 233, 235, 237, 241, 243, 247, 253, 259, 261, 267, 271, 273, 279, 283, 289

Offset

1,1

Comments

A105184 and A121609 are subsequences.

Links

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

G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 17257

Example

133 is in the sequence because 133 = 13*10+3 = A000040(6)*10+A000040(2).

Mathematica

nn=500; t=Union[Reap[Do[n=FromDigits[Join[IntegerDigits[Prime[i]], IntegerDigits[Prime[j]]]]; If[n<=nn, Sow[n]], {i, PrimePi[nn/10]}, {j, PrimePi[nn/IntegerDigits[nn][[1]]]}]][[2, 1]]] (* T. D. Noe, Mar 11 2011 *)

Prog

(Python)
from sympy import isprime
from itertools import count, islice
def agen(): # generator of terms
    for k in count(1):
        s = str(k)
        if any(s[i] != '0' and isprime(int(s[:i])) and isprime(int(s[i:])) for i in range(1, len(s))):
            yield k
print(list(islice(agen(), 55))) # Michael S. Branicky, Feb 26 2022

Crossrefs

Cf. A001358, A105184, A121609.

Sequence in context: A236404 A058814 A034895 * A092619 A092624 A254751

Adjacent sequences: A106579 A106580 A106581 * A106583 A106584 A106585

Keyword

base,nonn

Author

Eric Angelini and Robert G. Wilson v, May 09 2005

Extensions

Corrected by Arkadiusz Wesolowski, Mar 11 2011

Status

approved