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 A178388 #12 Aug 25 2022 12:37:24
%S A178388 2,210,21012,2101221,2101221102,2101221102111,2101221102111122,
%T A178388 2101221102111122201,2101221102111122201212,
%U A178388 21012211021111222012121002,210122110211112220121210021011,2101221102111122201212100210111101
%N A178388 Concatenation of the first n primes written in base 3.
%H A178388 Rémy Sigrist, <a href="/A178388/b178388.txt">Table of n, a(n) for n = 1..174</a>
%e A178388 a(4) = Concatenate[prime(1) base 3, prime(2) base 3, prime(3) base 3, prime(3) base 3] = Concatenate[2 base 3, 3 base 3, 5 base 3, 7 base 3] = Concatenate[2, 10, 12, 21] = 2101221.
%t A178388 Module[{nn=15,p3},p3=IntegerDigits[Prime[Range[nn]],3];Table[FromDigits[Flatten[ Take[p3,n]]],{n,nn}]] (* _Harvey P. Dale_, Aug 25 2022 *)
%o A178388 (PARI) v = 0; for (n=1, 12, d = digits(prime(n), 3); v = v*10^#d + fromdigits(d); print1 (v ", ")) \\ _Rémy Sigrist_, Aug 07 2017
%Y A178388 Cf. A000040, A001363, A004676, A007088, A007089, A019518, A031974, A100003, A154703.
%K A178388 base,easy,nonn
%O A178388 1,1
%A A178388 _Jonathan Vos Post_, May 26 2010
%E A178388 Edited by _N. J. A. Sloane_, Jul 02 2017