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A066401 Square root of b_1*b_2*...*b_t corresponding to smallest values of t in R. L. Graham's sequence (A006255). 5
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 (list; graph; refs; listen; history; text; internal format)
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: A242931 A110645 A064913 * A263538 A076590 A113660

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

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Last modified October 16 16:13 EDT 2019. Contains 328101 sequences. (Running on oeis4.)