A066401 Square root of b_1*b_2*...*b_t corresponding to smallest values of t in R. L. Graham's sequence (A006255).

1, 6, 12, 2, 20, 24, 28, 120, 3, 180, 66, 60, 78, 1260, 360, 4, 102, 108, 152, 120, 126, 132, 184, 144, 5, 936, 5040, 1120, 232, 210, 248, 240, 9240, 2040, 1680, 6, 370, 342, 312, 300, 410, 336, 430, 330, 360, 414, 470, 360, 7, 420, 25704, 196560, 636, 3780

Offset: 1

Author

N. J. A. Sloane, Dec 25 2001

Keywords

• nonn
• easy

Comments

a(n) = A000196(A245530(n)). - Reinhard Zumkeller, Jul 25 2014

Examples

			a(2) = 6 because the best such sequence is 2,3,6 for which the product is 36 = 6^2.
		

References

• R. L. Graham, D. E. Knuth and O. Patashnik, Concrete Mathematics. Addison-Wesley, Reading, MA, 1990, p. 147.

Links

• Peter Kagey, Table of n, a(n) for n = 1..1000 (First 125 terms from Reinhard Zumkeller)
• R. L. Graham, Bijection between integers and composites, Problem 1242, Math. Mag., 60 (1987), p. 180.

Crossrefs

Cf. A000196, A006255, A066400, A245499, A245530.

Programs

Haskell

a066401 = a000196 . a245530  -- Reinhard Zumkeller, Jul 25 2014

Mathematica

Table[k = 0; While[Length@ # == 0 &@ Set[f, Select[Rest@ Subsets@ Range@ k, IntegerQ@ Sqrt[n (Times @@ # &[n + #])] &]], k++]; If[IntegerQ@ Sqrt@ n, k = {n}, k = n + Prepend[First@ f, 0]]; Sqrt[Times @@ k], {n, 22}] (* Michael De Vlieger, Oct 26 2016 *)

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), Jan 06 2005

More terms from Joshua Zucker, May 18 2006