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

Author

N. J. A. Sloane, Jan 15 2002

Keywords

• nonn
• nice

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

Crossrefs

Cf. A066720, A066775.

Cf. A010051.

Programs

Haskell

a066721 n = a066721_list !! (n-1)
a066721_list = filter ((== 0) . a010051') a066720_list
-- Reinhard Zumkeller, Nov 19 2013

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[ ]] ]]

PARI

{a066721(m) = local(a,rat,n,s,new,b,i,k,j); a=[]; rat=Set([]); n=0; s=0; while(sKlaus Brockhaus, Feb 23 2002

Extensions

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