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A246801 Primes of the form: concatenation n with n-th composite integer. 2

%I

%S 4057,4463,4969,5881,6691,86117,90121,129169,131171,136177,160207,

%T 162209,169217,193247,225287,252319,265333,272341,280351,288361,

%U 297371,327407,346429,355441,388481,410507,429529,451553,456559,474581

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

%H Jens Kruse Andersen, <a href="/A246801/b246801.txt">Table of n, a(n) for n = 1..10000</a>

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

%t w = Select[Range[2, 800], ! PrimeQ[#] &]; Select[

%t Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[w[[n]]]}]], {n, 480}], PrimeQ]

%o (Python)

%o import sympy

%o from sympy import isprime

%o c = 0

%o for n in range(2,10**5):

%o ..if not isprime(n):

%o ....c += 1

%o ....p = str(c)+str(n)

%o ....if isprime(p):

%o ......print(int(p),end=', ')

%o # _Derek Orr_, Sep 18 2014

%Y Cf. A000040, A002808, A191992.

%K nonn,base

%O 1,1

%A _Jahangeer Kholdi_, Sep 15 2014

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Last modified June 13 07:45 EDT 2021. Contains 344981 sequences. (Running on oeis4.)