A066721 Nonprimes in A066720.

1, 8, 18, 50, 60, 81, 98, 105, 128, 242, 264, 308, 338, 416, 495, 520, 546, 560, 578, 625, 663, 675, 684, 864, 935, 952, 1029, 1058, 1083, 1224, 1242, 1254, 1425, 1430, 1682, 1729, 1748, 1771, 1827, 1922, 2436, 2691, 2697, 2720, 2738, 2755, 2790, 2975

Offset

1,2

Comments

2*p^2 is in the sequence for all primes except those in A066775.

Links

David Applegate, First 48186 terms of A066721

David Applegate, C program for computing this sequence

David Applegate, First 48186 terms of A066721 and their factorizations

Mathematica

s={1}; xok := Module[ {}, For[ i=1, i<=n, i++, For[ j=1; k=Length[ dl=Divisors[ s[[ i ]]x ]], j<=k, j++; k--, If[ MemberQ[ s, dl[[ j ] ]]&&MemberQ[ s, dl[[ k ] ]], Return[ False ]] ]]; True ]; For[ n=1, True, n++, If[ !PrimeQ[ s[[ n ] ]], Print[ s[[ n ]] ]]; For[ x=s[[ n ]]+1, True, x++, If[ xok, AppendTo[ s, x ]; Break[ ]] ]]

Prog

(PARI) {a066721(m) = local(a, rat, n, s, new, b, i, k, j); a=[]; rat=Set([]); n=0; s=0; while(s<m, s++; new=Set([]); b=1; i=1; while(b&&i<=n, k=s/a[i]; if(setsearch(rat, k), b=0, new=setunion(new, Set(k)); k=a[i]/s; if(setsearch(rat, k), b=0, new=setunion(new, Set(k)) )); i++); if(b, rat=setunion(rat, new); a=concat(a, s); n++; if(!isprime(s), print1(s, ", "))))} a066721(3000) \\ Klaus Brockhaus, Feb 23 2002
(Haskell)
a066721 n = a066721_list !! (n-1)
a066721_list = filter ((== 0) . a010051') a066720_list
-- Reinhard Zumkeller, Nov 19 2013

Crossrefs

Cf. A066720, A066775.

Cf. A010051.

Sequence in context: A153388 A109988 A335440 * A079704 A341528 A032795

Adjacent sequences: A066718 A066719 A066720 * A066722 A066723 A066724

Keyword

nonn,nice

Author

N. J. A. Sloane, Jan 15 2002

Extensions

More terms from Dean Hickerson, Klaus Brockhaus and David Applegate, Jan 15 2002

Status

approved