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
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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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 *)
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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