A336323 Numbers composite(n) such that gcd(n,composite(n)) > 1.

6, 10, 12, 14, 18, 21, 24, 25, 26, 28, 32, 33, 34, 36, 39, 42, 45, 48, 50, 52, 60, 68, 70, 72, 74, 76, 77, 78, 84, 86, 87, 88, 90, 95, 98, 100, 102, 104, 105, 106, 110, 111, 112, 124, 128, 130, 132, 135, 138, 140, 145, 147, 150, 158, 160, 162, 165, 168, 170

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = A002808(A334880(n)). - Michel Marcus, Jul 19 2020

Maple

compn:= 0: R:= NULL: count:= 0:
for n from 4 while count < 100 do
  if not isprime(n) then
    compn:= compn+1;
    if igcd(compn, n) > 1 then
      R:= R, n; count:= count+1;
    fi
  fi
od:
R; # Robert Israel, Aug 09 2020

Mathematica

c = Select[Range[2, 250], ! PrimeQ[#] &]; (*  A002808 *)
u = Select[Range[Length[c]], GCD[c[[#]], #] > 1 &] ; (* A334880 *)
Table[c[[u[[n]]]], {n, 1, Length[u]}] (* A336323 *)

Prog

(PARI) lista(nn) = {my(n=0, list=List()); forcomposite (c=1, nn, n++; if (gcd(n, c) > 1, listput(list, c))); Vec(list); } \\ Michel Marcus, Jul 19 2020

Crossrefs

Cf. A002808, A334880.

Sequence in context: A362012 A334166 A363171 * A175352 A175397 A129493

Adjacent sequences: A336320 A336321 A336322 * A336324 A336325 A336326

Keyword

nonn,easy

Author

Clark Kimberling, Jul 18 2020

Status

approved