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
Examples
4057 is in the sequence since 40th composite integer is 57 and 4057 is prime.
Links
- Jens Kruse Andersen, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
w = Select[Range[2, 800], ! PrimeQ[#] &]; Select[ Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[w[[n]]]}]], {n, 480}], PrimeQ] -
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