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 A251360 #50 May 16 2025 15:06:34
%S A251360 1117,2163,2537,5137,222926801
%N A251360 Numbers k such that k is the concatenation of prime factors of pi(k), in increasing order.
%C A251360 Numbers k such that k = A037276(A000720(k)).
%C A251360 Conjecture: numbers k such that k = A084317(A000720(k)). - _Chai Wah Wu_, Apr 04 2018
%C A251360 a(6) > 10^12 if exists. - _Max Alekseyev_, May 16 2025
%H A251360 Chris Caldwell, G. L. Honaker and Lewis, <a href="https://primes.utm.edu/curios/page.php/1117.html">1117</a>
%e A251360 1117 is in the sequence since pi(1117) = 11*17,
%e A251360 2163 is in the sequence since pi(2163) = 2*163,
%e A251360 2537 is in the sequence since pi(2537) = 2*5*37,
%e A251360 and 5137 is in the sequence since pi(5137) = 5*137.
%t A251360 a251360[n_Integer] := Select[Range[n], # == FromDigits[Flatten@IntegerDigits[First@ Transpose@ FactorInteger[PrimePi[#]]]] &]; a251360[10^5] (* _Michael De Vlieger_, Dec 03 2014 *)
%o A251360 (Python)
%o A251360 from sympy import prime, factorint
%o A251360 A251360_list, p = [], 3
%o A251360 for n in range(2,10**6):
%o A251360 q, fn = prime(n+1), factorint(n)
%o A251360 m = int(''.join(str(d)*fn[d] for d in sorted(fn)))
%o A251360 if p <= m < q:
%o A251360 A251360_list.append(m)
%o A251360 p = q # _Chai Wah Wu_, Dec 10 2014, corrected Apr 04 2018
%Y A251360 Cf. A000040, A000720, A251361, A251362.
%K A251360 nonn,base,more
%O A251360 1,1
%A A251360 _Jahangeer Kholdi_, Dec 01 2014
%E A251360 a(5) from _Chai Wah Wu_, Dec 10 2014