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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

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