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A106582
Numbers which are the concatenation of two primes.
8
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
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
KEYWORD
base,nonn
AUTHOR
EXTENSIONS
Corrected by Arkadiusz Wesolowski, Mar 11 2011
STATUS
approved