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

Author

Eric Angelini and Carole Dubois, Nov 07 2020

Keywords

• base
• nonn

Examples

			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).