A158215 Smallest palindromic prime made up of 0's and p(n) 1's, where p(n) is the n-th prime = A000040(n) (or 0 when no such prime exists).
11, 0, 100111001, 110111011, 1110111110111, 10111101110111101, 100111111111111111001, 1111111111111111111, 11111111111111111111111, 1111110111111111111111110111111, 11111101111111110101111111110111111
Offset: 1
Links
- Chai Wah Wu, Table of n, a(n) for n = 1..168
Crossrefs
Cf. A157712
Cf. A158214. [Lekraj Beedassy, Jun 21 2009]
Programs
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Python
from _future_ import division from itertools import combinations from sympy import prime, isprime def A158215(n): if n == 1: return 11 if n == 2: return 0 p2 = prime(n)//2 l = p2 while True: for i in combinations(range(l),l-p2): s = ['1']*l for x in i: s[x] = '0' s = ''.join(s) q = int(s+'1'+s[::-1]) if isprime(q): return q l += 1 # Chai Wah Wu, Nov 05 2015
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