A256048 Smallest palindromic prime by adding at least one digit to both the left and right of n.

101, 313, 727, 131, 11411, 151, 10601, 373, 181, 191, 30103, 1114111, 1120211, 11311, 11411, 31513, 1160611, 1117111, 18181, 71917, 30203, 1120211, 72227, 32323, 12421, 1250521, 36263, 12721, 12821, 39293, 10301, 11311, 32323, 13331, 14341, 33533, 16361, 77377

Offset: 0

Author

Felix Fröhlich, Mar 10 2015

Keywords

• nonn
• base

Links

• Chai Wah Wu, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A090287

Programs

Python

from _future_ import division
from sympy import isprime
def palgenrange2(m,l): # generator of odd-length palindromes of length at least m and at most 2*l
    if m == 1:
        yield 0
    for x in range(m//2+1,l+1):
        n = 10**(x-1)
        for y in range(n,n*10):
            s = str(y)
            yield int(s+s[-2::-1])
def A256048(n):
    sn = str(n)
    for p in palgenrange2(len(sn)+2,len(sn)+20):
        if sn in str(p)[1:-1] and isprime(p):
            break
    else:
        return 'search limit reached'
    return p # Chai Wah Wu, Mar 22 2015

Extensions

a(10), a(12), a(16), a(18) corrected by Chai Wah Wu, Mar 22 2015