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A338745
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When a(n) is even, a(n) is the number of prime digits present so far in the sequence, a(n) included.
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6
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1, 3, 2, 5, 7, 4, 9, 11, 13, 15, 6, 17, 19, 21, 8, 23, 10, 25, 27, 14, 29, 31, 16, 33, 18, 35, 22, 37, 39, 26, 41, 43, 28, 45, 30, 32, 47, 34, 49, 51, 36, 53, 55, 40, 57, 59, 61, 63, 44, 65, 67, 46, 69, 71, 73, 50, 52, 75, 77, 79, 58, 81, 83, 85, 60, 87, 62, 89, 91, 93, 95, 64, 97, 99, 101, 103, 66
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OFFSET
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1,2
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COMMENTS
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The prime digits are 2, 3, 5 and 7. The prime numbers appear in their natural order in the sequence [except for the switch a(2)<->a(3)]. Some nonprimes will never appear (12 for instance).
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LINKS
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EXAMPLE
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The first even term is a(3) = 2 and there are indeed 2 prime digits so far in the sequence (3 and 2 itself);
The next even term is a(6) = 4 and there are now 4 prime digits so far (3, 2, 5 and 7);
The next even term is a(11) = 6 and there are now 6 prime digits so far (3, 2, 5, 7, 3 and 5); etc.
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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