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A226011 Numbers n such that nonprime(n) divides n^2. 0
1, 2, 4, 18, 72, 130, 280, 495, 840, 900, 930, 1216, 1880, 2646, 3182, 3762, 17437, 21600, 29400, 30654, 35207, 45024, 58230, 266133, 1051980, 1204164, 1204320, 2193408, 2494520, 2549745, 3272178, 3671570, 3843378, 5166708, 5398785, 8709805, 8922270, 8922480 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..38.

EXAMPLE

The 4th nonprime is 8, and 8 divides 4^2 = 16, so 8 is in the sequence.

MAPLE

for n from 1 do

    if n^2 mod A018252(n) = 0 then

        print(n) ;

    end if;

end do: # R. J. Mathar, Jun 04 2013

MATHEMATICA

seq = {}; np = n = 0; p = 2; While[n < 10^5, If[++np == p, p = NextPrime@p, n++; If[Mod[n^2, np] == 0, Print@{n, np, n^2/np}; AppendTo[seq, n]]]]; seq (* Giovanni Resta, May 27 2013 *)

Module[{nn=10^7, np, len}, np=Complement[Range[nn], Prime[ Range[ PrimePi[ nn]]]]; len=Length[np]; Transpose[Select[ Thread[ {Range[len], np}], Divisible[ First[#]^2, Last[#]]&]][[1]]] (* Harvey P. Dale, Sep 10 2014 *)

CROSSREFS

Cf. A018252.

Sequence in context: A009679 A007727 A303352 * A325850 A052689 A139104

Adjacent sequences:  A226008 A226009 A226010 * A226012 A226013 A226014

KEYWORD

nonn,less

AUTHOR

Gerasimov Sergey, May 27 2013

EXTENSIONS

a(5)-a(38) from Giovanni Resta, May 27 2013

STATUS

approved

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Last modified December 15 20:00 EST 2019. Contains 330000 sequences. (Running on oeis4.)