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1,2

Exactly every other term, and also every other digit (in concatenated terms) is prime.

Table of n, a(n) for n=1..78.

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

The sequence A217559 is a simplified variant.

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

Sequence in context: A073846 A110458 A217559 * A114112 A113981 A234519

Adjacent sequences: A217557 A217558 A217559 * A217561 A217562 A217563

nonn,base

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

Values from a(26)=43 on corrected by J-M Falcoz, Oct 10 2012

approved