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 A117782 Total number of palindromic primes in base 6 with n digits. 1
 3, 1, 6, 0, 21, 0, 95, 0, 445, 0, 2181, 0, 11496, 0, 59723, 0, 315949, 0, 1718494, 0, 9403664, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Every palindrome with an even number of digits is divisible by 11 (in base 6) and therefore is composite (not prime). Hence there is only one palindromic prime with an even number of digits. A palindromic prime > 3 in base 6 must start (and end) with either the digit 1 or the digit 5. - Chai Wah Wu, Dec 03 2015 LINKS Eric Weisstein: Palindromic Prime. EXAMPLE a(2) = 1, because 11(6) = 7(10), is the only palindromic prime with 2 digits. - Michel Marcus, Oct 11 2014 MATHEMATICA Length@ Select[Prime@ Range[PrimePi[6^# + 1], PrimePi[6^(# + 1)]], # == Reverse@ # &@ IntegerDigits[#, 6] &] & /@ Range[0, 8] (* Michael De Vlieger, Dec 06 2015 *) PROG (PARI) a(nd, b=6) = {if ((nd > 2) && ((nd % 2) == 0), return (0)); nb = 0; forprime(p = b^(nd-1), b^nd-1, d = digits(p, b); if (Pol(d) == Polrev(d), nb++); ); nb; } \\ Michel Marcus, Oct 11 2014 CROSSREFS Cf. A029974, A117701. Sequence in context: A197151 A083238 A337604 * A317855 A301331 A301333 Adjacent sequences:  A117779 A117780 A117781 * A117783 A117784 A117785 KEYWORD nonn,base,more AUTHOR Martin Renner, Apr 15 2006 EXTENSIONS a(11)-a(12) from Michel Marcus, Oct 11 2014 a(13)-a(22) from Chai Wah Wu, Dec 03 2015 STATUS approved

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Last modified April 14 12:11 EDT 2021. Contains 342949 sequences. (Running on oeis4.)