(MAGMAMagma) S:=[]; a:=0; c:=0; for n in [1..20000000] do if not IsPrime(n) then a+:=n; c+:=1; if a mod c eq 0 then Append(~S, a); end if; end if; end for; S;

a(16)-a(19) from _Donovan Johnson (donovan.johnson(AT)yahoo.com), _, Sep 19 2009

a(20) from _Donovan Johnson (donovan.johnson(AT)yahoo.com), _, Jun 21 2011

_Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), _, Aug 11 2009

proposed

approved

1, 64, 800, 1452, 207143, 14934568, 18656679, 42721785, 889239450, 1991045973, 6684665064, 11847007536, 127880982508860, 262907426075600, 435646635220423, 58536266213035868, 1777764795352216572, 5690843954660983949, 190101452851104748107, 71537286176000166753366

a(19) = 190101452851104748107. [From Donovan Johnson (donovan.johnson(AT)yahoo.com), Sep 19 2009]

a(20) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jun 21 2011

approved

proposed

a(n) is the sum of the first A129749(n) nonprimes.

1, 64, 800, 1452, 207143, 14934568, 18656679, 42721785, 889239450, 1991045973, 6684665064, 11847007536, 127880982508860, 262907426075600, 435646635220423, 58536266213035868, 1777764795352216572, 5690843954660983949

1,2

A variant of A050247 for nonprimes.

a(19) = 190101452851104748107. [From Donovan Johnson (donovan.johnson(AT)yahoo.com), Sep 19 2009]

a(n) = sum_{i=1..A129749(n)} A018252(i).

A129749(4) = 44; sum of first 44 nonprimes is 1452, so a(4) = 1452.

(MAGMA) S:=[]; a:=0; c:=0; for n in [1..20000000] do if not IsPrime(n) then a+:=n; c+:=1; if a mod c eq 0 then Append(~S, a); end if; end if; end for; S;

Cf. A129749, A050247, A018252, A160758.

nonn

Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Aug 11 2009

a(16)-a(19) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Sep 19 2009

approved