A047947 a(n) is the number of k values for which A023193(k) = n.

2, 4, 2, 4, 4, 4, 6, 4, 2, 4, 6, 6, 2, 6, 4, 6, 4, 6, 4, 4, 6, 4, 6, 10, 4, 6, 6, 4, 6, 4, 6, 6, 4, 2, 4, 6, 8, 6, 4, 2, 8, 4, 10, 2, 4, 10, 10, 4, 6, 6, 2, 10, 6, 2, 6, 4, 6, 12, 4, 6, 10, 4, 6, 6, 6, 8, 6, 10, 4, 8, 6, 6, 2, 6, 12, 10, 2, 4, 6, 6, 8, 4, 2, 10, 8, 6, 6, 4, 8, 10, 2, 6, 4, 2

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Comments

The old name was: "Schinzel's rhobar(n), number of distinct lengths of a block of consecutive integers on which a maximum of n primes occurs infinitely often (under the k-tuple conjecture)." [Note that "rhobar" is A023193.]

Examples

			A block of 21 through 26 consecutive integers may contain at most 7 primes infinitely often. There are 6 possible lengths (21 through 26), so rhobar(7) = 6.
		

References

• Computed by Achim Flammenkamp.

Crossrefs

First differences of A020497. Cf. A008407, A023193.

Extensions

Definition corrected by Wolfdieter Lang, Oct 07 2017