A156761 Tribonacci primes that are also primes when their digits are reversed.

3, 5, 17, 31, 1201, 128199521

Offset: 1

Author

Jonathan Vos Post, Feb 15 2009

Keywords

• more
• nonn
• base

Comments

This is to A115347 as Fibonacci numbers A000045 are to A000213 tribonacci numbers. Except for palidromatic tribonacci numbers {3, 5, ...} these are tribonacci emirps, A000213 INTERSECTION A006567.

a(7), if it exists, is greater than A000213(10000). - Dmitry Kamenetsky, Mar 03 2009

a(7), if it exists, is greater than A000213(116404), testing tribonacci primes using A157611. - Michael S. Branicky, May 27 2025

Examples

			a(5) = 1201 because 1201 is prime, and is the 13th tribonacci number A000213(13), and R(1201) = A004086(1201) = 1021 is also prime. a(6) = 128199521 = the 10th tribonacci prime A056816(10), and its digital reverse 125991821 is also prime.
		

Crossrefs

Cf. A000040, A000045, A000213, A004086, A006567, A056816, A115347, A157611.

Programs

Mathematica

Select[LinearRecurrence[{1,1,1},{1,1,1},200],AllTrue[{#,IntegerReverse[ #]},PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 31 2019 *)

Formula

{p such that p is in A000040 and p is in A000213 and R(p) = A004086(p) is in A000040} = {p such that p is in A056816 and R(p) = is in A000040}.