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

1,2

Comments

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

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.

Example

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

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 *)

Prog

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

Crossrefs

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

Sequence in context: A341828 A110645 A064913 * A335413 A356119 A263538

Adjacent sequences: A066398 A066399 A066400 * A066402 A066403 A066404

Keyword

nonn,easy

Author

N. J. A. Sloane, Dec 25 2001

Extensions

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

More terms from Joshua Zucker, May 18 2006

Status

approved