A052092 - OEIS

%I #18 Dec 04 2015 04:12:40

%S 1,3,5,9,11,15,19,23,25,31,35,41,45,49,55,59,63,69,75,81,87,93,99,105,

%T 109,113,119,125,129,133,139,145,151,157,161,167,173,179,185,191,195,

%U 201,207,213,219,225,231,237,243,249,255,261,267,273,279,285,291,297

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

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

%C 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

%H Chai Wah Wu, <a href="/A052092/b052092.txt">Table of n, a(n) for n = 0..501</a>

%o (Python)

%o from sympy import isprime

%o A052092_list, l, p = [1], 1, 2

%o for _ in range(100):

%o     m, ps = 1, str(p)

%o     s = int('1'+ps+'1')

%o     while not isprime(s):

%o         m += 1

%o         ms = str(m)

%o         if ms[0] in '268':

%o             ms = str(int(ms[0])+1) + '0'*(len(ms)-1)

%o             m = int(ms)

%o         if ms[0] in '45':

%o             ms = '7' + '0'*(len(ms)-1)

%o             m = int(ms)

%o         s = int(ms+ps+ms[::-1])

%o     p = s

%o     l += 2*len(ms)

%o     A052092_list.append(l) # _Chai Wah Wu_, Dec 02 2015

%Y Cf. A052091, A053600, A047076.

%K nonn,base

%O 0,2

%A _Patrick De Geest_, Jan 15 2000

%E Comments from _G. L. Honaker, Jr._, Mar 30 2000

%E Edited by _T. D. Noe_, Oct 30 2008