A103835 Smallest prime p, larger than previous term, such that concatenation of n and p is a prime.

3, 11, 13, 19, 23, 31, 43, 53, 67, 97, 113, 149, 151, 173, 193, 223, 239, 251, 373, 389, 397, 409, 431, 439, 457, 479, 487, 499, 569, 577, 601, 647, 739, 757, 797, 809, 811, 821, 827, 829, 863, 929, 991, 1109, 1181, 1297, 1301, 1303, 1327, 1367, 1409, 1429

Offset

1,1

Comments

Cf. A096915

Links

Table of n, a(n) for n=1..52.

Example

a(10)=97 because 1097 is prime, while 1071,1073,1079,1083,1089 are all composite.

Prog

(Python)
from sympy import isprime, nextprime
def ispal(n): s = str(n); return s == s[::-1]
def aupto(lim):
  n, p, alst = 1, 2, []
  while p <= lim:
    if isprime(int(str(n)+str(p))): n, alst = n + 1, alst + [p]
    p = nextprime(p)
  return alst
print(aupto(1429)) # Michael S. Branicky, Mar 11 2021

Crossrefs

Cf. A096915, A103836.

Sequence in context: A045428 A338445 A191049 * A067386 A063621 A176870

Adjacent sequences: A103832 A103833 A103834 * A103836 A103837 A103838

Keyword

nonn,base

Author

Zak Seidov, Mar 30 2005

Status

approved