A139805 - OEIS

A139805

A number n is included if (product{k|n, k<=sqrt(n)} k) (= A072499(n)) does not divide n.

20, 28, 36, 42, 44, 48, 52, 54, 60, 66, 68, 72, 76, 78, 80, 84, 88, 90, 92, 96, 99, 100, 102, 104, 108, 110, 112, 114, 116, 117, 120, 124, 126, 130, 132, 136, 138, 140, 144, 148, 150, 152, 153, 156, 160, 162, 164, 168, 170, 171, 172, 174, 176, 180, 184, 186, 188

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..57.

EXAMPLE

The divisors of 42 that are each <= sqrt(42) are 1,2,3,6. The product of these is 36. 36 does not divide 42, so 42 is in the sequence.

MAPLE

A072499 := proc(n) local a, k ; a := 1 ; for k in numtheory[divisors](n) do if k^2 <= n then a := a*k ; fi ; od: a ; end: isA139805 := proc(n) RETURN( n mod A072499(n) <> 0 ) end: for n from 1 to 300 do if isA139805(n) then printf("%d, ", n) ; fi ; od: # R. J. Mathar, May 24 2008

MATHEMATICA

a = {}; For[n = 1, n < 200, n++, If[Mod[n, Times @@ (Select[Divisors[n], ! # > Sqrt[n] &])] > 0, AppendTo[a, n]]]; a (* Stefan Steinerberger *)

CROSSREFS

Cf. A072499.

Sequence in context: A032482 A024411 A269986 * A141823 A367632 A137428

Adjacent sequences: A139802 A139803 A139804 * A139806 A139807 A139808

KEYWORD

nonn

AUTHOR

Leroy Quet, May 22 2008

EXTENSIONS

More terms from R. J. Mathar and Stefan Steinerberger, May 24 2008

STATUS

approved