A103836 Smallest palindromic prime p, larger than previous term, such that concatenation of n and p is a prime.

3, 11, 181, 373, 12821, 14741, 32323, 72227, 74747, 77977, 78887, 79997, 90709, 94049, 94849, 98689, 1055501, 1065601, 1114111, 1129211, 1134311, 1177711, 1180811, 1186811, 1190911, 1262621, 1333331, 1338331, 1407041, 1409041, 1411141, 1461641, 1463641

Offset: 1

Author

Zak Seidov, Mar 30 2005

Keywords

• nonn
• base

Comments

Cf. A096915

Examples

			a(4) = 373 because 4373 is prime, while 4191, 4313, 4353 are all composite.
		

Crossrefs

Cf. A096915, A103835.

Subsequence of A002385.

Programs

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 ispal(p) and isprime(int(str(n)+str(p))): n, alst = n + 1, alst + [p]
    p = nextprime(p)
  return alst
print(aupto(1463641)) # Michael S. Branicky, Mar 11 2021