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

0,1

Links

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

Prog

(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

Crossrefs

Cf. A090287

Sequence in context: A139701 A195294 A142578 * A252942 A090287 A134971

Adjacent sequences: A256045 A256046 A256047 * A256049 A256050 A256051

Keyword

nonn,base

Author

Felix Fröhlich, Mar 10 2015

Extensions

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

Status

approved