OFFSET
3,1
COMMENTS
LINKS
Daniel Suteu, Table of n, a(n) for n = 3..6587
Wikipedia, Truncatable prime
EXAMPLE
Rows for n = 3..7:
[2, 23]
[2, 3, 11]
[2, 3, 13, 17, 67]
[2, 3, 5, 17, 23, 83, 191, 479, 839]
[2, 3, 5, 17, 19, 23, 37]
PROG
(PARI)
digitsToNum(d, base) = sum(k=1, #d, base^(k-1) * d[k]);
isLeftTruncatable(d, base) = my(ok=1); for(k=1, #d, if(!isprime(digitsToNum(d[1..k], base)), ok=0; break)); ok;
generateFromPrefix(p, base) = my(seq = [p]); for(n=1, base-1, my(t=concat(n, p)); if(isprime(digitsToNum(t, base)), seq=concat(seq, select(v -> isLeftTruncatable(v, base), generateFromPrefix(t, base))))); seq;
bothTruncatablePrimesInBase(base) = my(t=[]); my(P=primes(primepi(base-1))); for(k=1, #P, t=concat(t, generateFromPrefix([P[k]], base))); vector(#t, k, digitsToNum(t[k], base));
row(n) = vecsort(bothTruncatablePrimesInBase(n));
T(n, k) = row(n)[k];
CROSSREFS
KEYWORD
AUTHOR
Daniel Suteu and Felix Fröhlich, Jan 13 2019
STATUS
approved