A225745 Smallest k such that n numbers can be picked in {1,...,k} with no four in arithmetic progression.

1, 2, 3, 5, 6, 8, 9, 10, 13, 15, 17, 19, 21, 23, 25, 27, 28, 30, 33, 34, 37, 40, 43, 45, 48, 50, 53, 54, 58, 60, 64, 66, 68, 70, 74, 77, 79, 82, 84, 87, 91

Offset: 1

Author

Don Knuth, Aug 05 2013

Keywords

• nonn
• more

Examples

			a(8)=10 because of the unique solution 1 2 3 5 6 8 9 10.
		

References

• Knuth, Donald E., Satisfiability, Fascicle 6, volume 4 of The Art of Computer Programming. Addison-Wesley, 2015, pages 135 and 190, Problem 31.

Links

• Samuel S. Wagstaff, Jr., On k-free sequences of integers, Math. Comp., 26 (1972), 767-771.

Crossrefs

This sequence is to A003003 as A065825 is to A003002.

Extensions

a(37)-a(41) from Bert Dobbelaere, Sep 16 2020