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

1,2

Links

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

Example

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.

Crossrefs

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

Sequence in context: A352808 A076990 A330434 * A057168 A087711 A123128

Adjacent sequences: A330421 A330422 A330423 * A330425 A330426 A330427

Keyword

base,nonn

Author

Eric Angelini and Lars Blomberg, Dec 14 2019

Status

approved