A166402 Composite terms of sequence A166401.

4, 8, 9, 16, 18, 25, 27, 32, 36, 49, 50, 64, 75, 81, 98, 100, 121, 125, 128, 144, 147, 162, 169, 196, 200, 225, 242, 243, 245, 256, 289, 324, 338, 343, 361, 363, 392, 400, 441, 484, 507, 512, 529, 576, 578, 605, 625, 676, 722, 729, 784, 841, 845, 847, 867, 882

Offset

1,1

Comments

Sequence A166401 contains 1 and all the primes in addition to this sequence's terms. For those terms that are not powers of primes, see A166403.

Links

Ivan Neretin, Table of n, a(n) for n = 1..10000

Maple

filter:= proc(n) local a, b;
   if isprime(n) then return false fi;
   if issqr(n) then return true fi;
   a, b:= selectremove(t -> (t^2 <= n), numtheory:-divisors(n));
   min(b) mod max(a) = 0
end proc:
select(filter, [$4..1000]); # Robert Israel, Jan 13 2016

Mathematica

Select[Range[2, 900], ! PrimeQ[#] && Divisible[(d = Divisors[#])[[n = Floor[Length[d]/2 + 1]]], d[[-n]]] &] (* Ivan Neretin, Jan 12 2016 *)

Crossrefs

Cf. A166401, A166403

Sequence in context: A325661 A073539 A090779 * A255586 A034038 A069265

Adjacent sequences: A166399 A166400 A166401 * A166403 A166404 A166405

Keyword

nonn

Author

Leroy Quet, Oct 13 2009

Extensions

More terms from Max Alekseyev, Feb 21 2010

Status

approved