This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A246801 #33 Jun 23 2025 17:26:03
%S A246801 4057,4463,4969,5881,6691,86117,90121,129169,131171,136177,160207,
%T A246801 162209,169217,193247,225287,252319,265333,272341,280351,288361,
%U A246801 297371,327407,346429,355441,388481,410507,429529,451553,456559,474581
%N A246801 Primes of the form: concatenation n with n-th composite integer.
%H A246801 Jens Kruse Andersen, <a href="/A246801/b246801.txt">Table of n, a(n) for n = 1..10000</a>
%e A246801 4057 is in the sequence since 40th composite integer is 57 and 4057 is prime.
%t A246801 w = Select[Range[2, 800], ! PrimeQ[#] &]; Select[
%t A246801 Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[w[[n]]]}]], {n, 480}], PrimeQ]
%o A246801 (Python)
%o A246801 import sympy
%o A246801 from sympy import isprime
%o A246801 c = 0
%o A246801 for n in range(2,10**5):
%o A246801 if not isprime(n):
%o A246801 c += 1
%o A246801 p = int(str(c)+str(n))
%o A246801 if isprime(p):
%o A246801 print(p,end=', ')
%o A246801 # _Derek Orr_, Sep 18 2014
%Y A246801 Cf. A000040, A002808, A191992.
%K A246801 nonn,base
%O A246801 1,1
%A A246801 _Jahangeer Kholdi_, Sep 15 2014