cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A117775 Total number of palindromic primes in base 3 below 3^n.

Original entry on oeis.org

1, 1, 3, 3, 6, 6, 18, 18, 26, 26, 73, 73, 179, 179, 459, 459, 1179, 1179, 3004, 3004, 8111, 8111, 22183, 22183, 60789, 60789, 168641, 168641, 469689, 469689, 1322664, 1322664, 3691761, 3691761, 10390938, 10390938, 29502559, 29502559, 84012658, 84012658, 239417332, 239417332
Offset: 1

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Author

Martin Renner, Apr 15 2006

Keywords

Comments

Every palindrome with an even number of digits is divisible by 11 (in base 3) and therefore is composite (not prime). Hence there is no palindromic prime with an even number of digits.

Examples

			a(5) = a(6) = 6 as the six palindromic primes below 3^5 are 2_10 = 2_3, 13_10 = 111_3, 23_10 = 212_3, 151_10 = 12121_3, 173_10 = 20102_3, 233_10 = 22122_3. There are no palindromic primes with 6 digits so a(5) = a(6). - _David A. Corneth_, Mar 21 2021

Links

Crossrefs

Partial sums of A117776.
Cf. A029971, A117698.
Cf. A117772, A117777, A117779, A117781, A117783, A117785, A117787.

Formula

a(2*k-1) = a(2*k) for k >= 1. - Bernard Schott, Mar 23 2021

Extensions

a(15)-a(42) from the data at A117776 added by Amiram Eldar, Mar 21 2021
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