A338746 When a(n) is odd, a(n) is the number of prime digits present so far in the sequence, a(n) included.

2, 1, 4, 6, 8, 10, 12, 3, 14, 16, 18, 20, 5, 22, 24, 26, 9, 28, 30, 11, 32, 34, 15, 36, 17, 38, 40, 42, 19, 44, 46, 48, 50, 21, 23, 25, 27, 52, 54, 31, 33, 35, 37, 56, 39, 58, 60, 62, 41, 64, 66, 68, 70, 43, 72, 74, 47, 76, 78, 49, 80, 82, 51, 53, 55, 57, 84, 86, 88, 90, 92, 59, 94, 96, 98, 100, 102

Offset

1,1

Links

Table of n, a(n) for n=1..77.

Example

The first odd term is a(2) = 1 and there is indeed 1 prime digit so far in the sequence (this is the 2 before 1);
The next odd term is a(8) = 3 and there are now 3 prime digits so far (2, 2 and 3);
The next odd term is a(13) = 5 and there are now 5 prime digits so far (2, 2, 3, 2 and 5); etc.

Crossrefs

Cf. A338741, A338742, A338743, A338744, A338745 (variants on the same idea).

Sequence in context: A335919 A296340 A048213 * A283309 A366043 A054408

Adjacent sequences: A338743 A338744 A338745 * A338747 A338748 A338749

Keyword

base,nonn

Author

Eric Angelini and Carole Dubois, Nov 07 2020

Status

approved