A052092 Lengths of the palindromic primes from Honaker's sequence A053600.

1, 3, 5, 9, 11, 15, 19, 23, 25, 31, 35, 41, 45, 49, 55, 59, 63, 69, 75, 81, 87, 93, 99, 105, 109, 113, 119, 125, 129, 133, 139, 145, 151, 157, 161, 167, 173, 179, 185, 191, 195, 201, 207, 213, 219, 225, 231, 237, 243, 249, 255, 261, 267, 273, 279, 285, 291, 297

Offset

0,2

Comments

Since the terms from a(34) onward are currently only probable primes, the lengths given in this sequence beyond that point are only provisional.

For n > 0, a(n) = a(n-1)+2*m where m is the number of digits of A052091(n). - Chai Wah Wu, Dec 03 2015

Links

Chai Wah Wu, Table of n, a(n) for n = 0..501

Prog

(Python)
from sympy import isprime
A052092_list, l, p = [1], 1, 2
for _ in range(100):
    m, ps = 1, str(p)
    s = int('1'+ps+'1')
    while not isprime(s):
        m += 1
        ms = str(m)
        if ms[0] in '268':
            ms = str(int(ms[0])+1) + '0'*(len(ms)-1)
            m = int(ms)
        if ms[0] in '45':
            ms = '7' + '0'*(len(ms)-1)
            m = int(ms)
        s = int(ms+ps+ms[::-1])
    p = s
    l += 2*len(ms)
    A052092_list.append(l) # Chai Wah Wu, Dec 02 2015

Crossrefs

Cf. A052091, A053600, A047076.

Sequence in context: A287421 A214214 A281505 * A075991 A292918 A216091

Adjacent sequences: A052089 A052090 A052091 * A052093 A052094 A052095

Keyword

nonn,base

Author

Patrick De Geest, Jan 15 2000

Extensions

Comments from G. L. Honaker, Jr., Mar 30 2000

Edited by T. D. Noe, Oct 30 2008

Status

approved