A226011 Numbers k such that nonprime(k) divides k^2.

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

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 * A174085 A325850 A052689

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