Number of left- or right-truncatable primes in base n.
10, 69, 49, 5599, 140, 4283, 1211, 149677, 1202, 6828095, 5224, 2367795, 630943, 3648155, 24649
3
Is the number infinity for some n? How would that be proved?
T. D. Noe, Plot of terms 3..17
See references in A137812.
(Mma) Table[Clear[s]; n = 0; s[n] = Prime[Range[PrimePi[b-1]]]; While[cnt = 0; lst = Reap[Do[k = s[n][[i]]; Do[p = j*b^(n+1) + k; If[PrimeQ[p], Sow[p]; cnt++], {j, b-1}]; Do[p = b*k + j; If[PrimeQ[p], Sow[p]; cnt++], {j, b-1}], {i, Length[s[n]]}]]; cnt > 0, n++; s[n] = Union[lst[[2,1]]]]; t = s[0]; Do[t = Join[t, s[i]], {i, n}]; Length[t], {b, 3, 11}]
Cf. A137812 (base 10), S000910-S000916 (bases 9 to 3).
nonn,base,hard,more
T. D. Noe, Jun 21 2016