A186711 Greatest common divisor of the n-th and (n+1)st 3-smooth numbers.

1, 1, 1, 2, 2, 1, 3, 4, 2, 6, 3, 1, 4, 12, 6, 2, 8, 9, 3, 12, 4, 16, 18, 6, 24, 27, 1, 32, 36, 12, 48, 54, 2, 64, 72, 81, 3, 96, 108, 4, 128, 144, 162, 6, 192, 216, 8, 1, 9, 288, 324, 12, 384, 432, 16, 2, 18, 576, 648, 24, 3, 27, 864, 32, 4, 36, 1152, 1296, 48, 6, 54, 1728, 64, 8, 72, 9, 81, 2592, 96, 12

Offset: 1

Author

Reinhard Zumkeller, Feb 26 2011

Keywords

• nonn

Comments

A186712 shows where this function and the 3-smooth numbers A003586 are in the same range: a(A186712(n)) = A003586(n) and a(m) != A003586(n) for m < A186712(n).

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A003586, A050873, A061987, A186771.

Programs

Haskell

a186711 n = a186711_list !! (n-1)
a186711_list = zipWith gcd a003586_list $ tail a003586_list

Maple

A186711 := proc(n) igcd(A003586(n),A003586(n+1)) ; end proc: # R. J. Mathar, Feb 28 2011

Mathematica

S3 = Select[Range[3*10^4], FactorInteger[#][[-1, 1]] <= 3&]; Table[GCD[ S3[[n]], S3[[n+1]] ], {n, 1, Length[S3]-1}] (* Jean-François Alcover, Feb 02 2018 *)

Formula

a(n) = A050873(A003586(n+1), A003586(n)).

a(A186771(n)) = 1.