A217559 Terms as well as ending/starting digits have alternating primality; this is the lexicographically earliest injective sequence with this property.

1, 2, 4, 3, 6, 5, 8, 7, 9, 23, 10, 29, 22, 11, 24, 31, 25, 13, 12, 17, 14, 37, 15, 19, 26, 53, 16, 59, 28, 71, 30, 73, 18, 79, 20, 211, 21, 223, 48, 227, 49, 229, 27, 41, 32, 43, 44, 233, 45, 47, 46, 239, 33, 61, 34, 241, 35, 67, 60, 251, 36, 257, 62, 83, 63, 89, 38, 263, 64, 269, 39, 271, 50, 277

Offset: 1

Author

Eric Angelini and M. F. Hasler, Oct 06 2012

Keywords

• nonn
• base

Comments

Exactly every other term is prime; moreover the ending digit of a(n) and the initial digit of a(n+1) are never both prime or both composite.

Links

• E. Angelini, Non-primes/primes: integers and digits alternate, SeqFan mailing list, Oct 06 2012

Crossrefs

This is a simplified variant of A217560.

See also A217555, A217556, where "primality" is replaced by "parity".

Programs

PARI

A217559(n,show_all=0,a=1,u)={for( i=2, n, u+=1<