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 A329027 #13 Mar 13 2024 01:50:57
%S A329027 0,2,0,1,0,2,2,2,0,3,0,1,3,3,0,1,0,1,2,2,0,1,0,1,2,2,0,1,0,2,2,2,2,3,
%T A329027 3,2,2,2,0,3,0,3,3,3,0,3,0,2,2,2,0,4,0,2,2,2,0,3,0,1,3,3,3,1,3,3,3,3,
%U A329027 0,3,0,1,3,3,0,1,0,1,4,4,0,1,0,1,3,3,0,1,0,1,2,2,2,1,4,2,2,2,0,4,0,1,4,4,0
%N A329027 The least missing digit in the primorial base expansion of n. Only significant digits are considered, as the leading zeros are ignored.
%C A329027 For n = 0 the value is ambiguous, thus the sequence starts from n=1.
%H A329027 Antti Karttunen, <a href="/A329027/b329027.txt">Table of n, a(n) for n = 1..32768</a>
%H A329027 <a href="/index/Pri#primorialbase">Index entries for sequences related to primorial base</a>.
%e A329027 19 in primorial base (A049345) is written as "301". The least missing digit is 2, thus a(19) = 2.
%t A329027 a[n_] := Module[{k = n, p = 2, s = {}, r}, While[{k, r} = QuotientRemainder[k, p]; k != 0 || r != 0, AppendTo[s, r]; p = NextPrime[p]]; Min[Complement[Range[0, Max[s]+1], s]]]; Array[a, 100] (* _Amiram Eldar_, Mar 13 2024 *)
%o A329027 (PARI) A329027(n) = { my(m=Map(), p=2); while(n, mapput(m,(n%p),1); n = n\p; p = nextprime(1+p)); for(k=0,oo,if(!mapisdefined(m,k),return(k))); };
%Y A329027 Cf. A049345, A329028.
%Y A329027 Cf. A328574 (after its initial term, gives the positions of zeros in this sequence), A328840 (after its initial term, gives the positions of ones in this sequence).
%K A329027 nonn,base
%O A329027 1,2
%A A329027 _Antti Karttunen_, Nov 03 2019