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A066721 Nonprimes in A066720. 3
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 (list; graph; refs; listen; history; text; internal format)
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: A034714 A153388 A109988 * A079704 A032795 A120543

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

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Last modified May 19 17:10 EDT 2019. Contains 323395 sequences. (Running on oeis4.)