A330424 a(1) = 1, a(2) = 2; thereafter a(n) = smallest number not occurring earlier such that both the sum of three successive terms and the sum of three successive digits are prime numbers.

1, 2, 4, 5, 8, 6, 3, 20, 14, 25, 44, 34, 49, 68, 32, 27, 24, 10, 67, 60, 12, 29, 26, 52, 41065, 62, 50, 61, 40, 30, 43, 64, 72, 21, 46, 16, 41, 22, 38, 23, 28, 122, 7, 82, 18, 81, 2012, 218, 21021, 84, 58, 69, 2002, 90, 201, 106, 76, 47, 88, 128, 1223, 2038

Offset: 1

Author

Eric Angelini and Lars Blomberg, Dec 14 2019

Keywords

• base
• nonn

Examples

			After 8 and 6 the next term is 3 as 8+6+3 = 17 is a prime;
after 6 and 3 the next term is 20 as 6+3+20 = 29 and 6+3+2=11 are both primes;
after 3 and 20 the next term is 14 as 3+20+14 = 37 and 3+2+0=5 are both primes;
etc.
		

Links

• Lars Blomberg, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A076990 (only the sum of three successive terms is prime).