A246801 Primes of the form: concatenation n with n-th composite integer.

4057, 4463, 4969, 5881, 6691, 86117, 90121, 129169, 131171, 136177, 160207, 162209, 169217, 193247, 225287, 252319, 265333, 272341, 280351, 288361, 297371, 327407, 346429, 355441, 388481, 410507, 429529, 451553, 456559, 474581

Offset

1,1

Links

Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

Example

4057 is in the sequence since 40th composite integer is 57 and 4057 is prime.

Mathematica

w = Select[Range[2, 800], ! PrimeQ[#] &]; Select[
Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[w[[n]]]}]], {n, 480}], PrimeQ]

Prog

(Python)
import sympy
from sympy import isprime
c = 0
for n in range(2, 10**5):
  if not isprime(n):
    c += 1
    p = int(str(c)+str(n))
    if isprime(p):
      print(p, end=', ')
# Derek Orr, Sep 18 2014

Crossrefs

Cf. A000040, A002808, A191992.

Sequence in context: A108006 A320207 A320216 * A020430 A163010 A069332

Adjacent sequences: A246798 A246799 A246800 * A246802 A246803 A246804

Keyword

nonn,base

Author

Jahangeer Kholdi, Sep 15 2014

Status

approved