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.
k = 4; Do[l = Table[ Prime[i], {i, 1, n}]; While[ PrimeQ[k] || Union[PowerMod[l, k - 1, k]] != {1}, k++ ]; Print[k], {n, 1, 29}]
isps(k, n) = {if (isprime(k), return (0)); my(nbok = 0); for (b=2, prime(n), if (Mod(b, k)^(k-1) == 1, nbok++, break)); if (nbok==prime(n)-1, return (1));}
a(n) = {my(k=2); while (!isps(k, n), k++); return (k);} \\ Michel Marcus, Apr 27 2018
a(n) = forcomposite(c=1, , my(i=0); for(b=2, n, if(Mod(b, c)^(c-1)==1, i++)); if(i==n-1, return(c)));
f[1] = 341; f[2] = 1105; f[3] = 1729; f[n_] := f[n] = Block[{k = f[n -1], lp = Prime@ Range[2, n -1], p = Prime@ n}, While[ PrimeQ@ k || PowerMod[2, k -1, k] != 1 || PowerMod[p, k -1, k] != 1 || Union[ PowerMod[lp, k -1, k]] != {1}, k += 2]; k]; Union[ Table[ f@n, {n, 1012}]]
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