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.
In base 1, n =11...11=n written n times; in base 0 baseform is taken as 0.
Table[BaseForm[w, Mod[w, 10]], {w, 1, 128}]
Eventually non-decimal digit symbols appear, as in case of 307=17d, in base 14 = 307 mod 293.
a:= proc(n) local b, p, l;
p:= ithprime(n); b:= irem(p, prevprime(p));
if b=1 then l:= 1$p
else l:= ""; while p>0 do l:= irem(p, b, 'p'), l od
fi; parse(cat(l))
end:
seq(a(n), n=2..62); # Alois P. Heinz, Sep 05 2019
Table[BaseForm[Prime[w], Mod[Prime[w], Prime[w-1]]], {w, 2, 128}]
Join[{111},FromDigits[IntegerDigits[#[[2]],Mod[#[[2]],#[[1]]]]]&/@ Partition[ Prime[Range[2,50]],2,1]] (* Harvey P. Dale, Jul 03 2021 *)
a(n) = {my(p=prime(n), q=prime(n-1)); if ((p % q) != 1, d=digits(p, p % q); if (#select(x->(x>9), d), 0, fromdigits(d, 10)), fromdigits(vector(p, k, 1), 10));} \\ Michel Marcus, Sep 05 2019
41 = 25 + 3*5 + 1 = 131_5.
Do[s=Prime[n]; If[Mod[s, 6]==5, Print[BaseForm[s, 5]]], {n, 1, 256}]
FromDigits[IntegerDigits[#, 5]] & /@ Select[Table[6 n + 5, {n, 0, 100}], PrimeQ] (* Harvey P. Dale, Oct 05 2023 *)
lista(nn) = for (n=0, nn, if (isprime(p=6*n+5), print1(fromdigits(digits(p, 5)), ", "))); \\ Michel Marcus, Jul 09 2018