A380010 Beginning with 7, least prime such that concatenation of the first n terms is prime.

7, 3, 3, 3, 31, 23, 13, 3, 167, 13, 137, 3, 73, 383, 499, 431, 13, 101, 61, 47, 67, 101, 13, 83, 1237, 107, 97, 467, 499, 677, 1423, 353, 73, 431, 331, 683, 487, 2141, 3, 1753, 1787, 31, 443, 139, 653, 1327, 17, 919, 173, 2851, 137, 547, 557, 5167, 347, 7867, 839, 19, 179, 19

Offset

1,1

Links

J.W.L. (Jan) Eerland, Table of n, a(n) for n = 1..1000

Mathematica

w={7}; Do[k=1; q=Monitor[Parallelize[While[True, If[PrimeQ[FromDigits[Join@@IntegerDigits/@Append[w, Prime[k]]]], Break[]]; k++]; Prime[k]], k]; w=Append[w, q], {i, 2, 50}]; w

Prog

(Python)
from itertools import count, islice
from gmpy2 import digits, is_prime, mpz, next_prime
def agen(): # generator of terms
    s, an = "", 7
    while True:
        yield int(an)
        s += digits(an)
        p = 3
        while not is_prime(mpz(s+digits(p))): p = next_prime(p)
        an = p
print(list(islice(agen(), 50))) # after Michael S. Branicky in A379354

Crossrefs

Cf. A111382, A111383, A113584, A379354, A379355, A379761, A380011.

Sequence in context: A021581 A265411 A393948 * A176833 A154019 A011299

Adjacent sequences: A380007 A380008 A380009 * A380011 A380012 A380013

Keyword

base,nonn

Author

J.W.L. (Jan) Eerland, Jan 09 2025

Status

approved