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A338746
When a(n) is odd, a(n) is the number of prime digits present so far in the sequence, a(n) included.
6
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
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
KEYWORD
base,nonn
AUTHOR
Eric Angelini and Carole Dubois, Nov 07 2020
STATUS
approved