

A217559


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


4



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
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OFFSET

1,2


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

Table of n, a(n) for n=1..74.
E. Angelini, Nonprimes/primes: integers and digits alternate, SeqFan mailing list, Oct 06 2012


PROG

(PARI) A217559(n, show_all=0, a=1, u)={for( i=2, n, u+=1<<a; show_all & print1(a", "); for(t=1, 9e9, bittest(u, t) & next; isprime(t)==bittest(i, 0) & next; isprime(a%10) == isprime(t\10^(#Str(t)1)) & (t+=10^(#Str(t)1)1) & next; a=t; break )); a}


CROSSREFS

This is a simplified variant of A217560.
See also A217555, A217556, where "primality" is replaced by "parity".
Sequence in context: A067747 A073846 A110458 * A217560 A114112 A113981
Adjacent sequences: A217556 A217557 A217558 * A217560 A217561 A217562


KEYWORD

nonn,base


AUTHOR

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


STATUS

approved



