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a(n) is the smallest positive multiple of {the n-th composite} that is greater than the n-th prime.
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%I #15 Mar 01 2019 23:34:15

%S 4,6,8,9,20,24,28,30,32,36,40,42,44,48,50,78,81,84,90,96,99,102,105,

%T 108,114,117,120,126,132,135,138,144,147,150,153,156,162,165,168,228,

%U 232,240,248,252,256,260,264,272,276,280,288,296,300,304,308,312,320,324

%N a(n) is the smallest positive multiple of {the n-th composite} that is greater than the n-th prime.

%H Harvey P. Dale, <a href="/A162738/b162738.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = ceiling(p(n)/c(n))*c(n), where c(n) is the n-th composite, and p(n) is the n-th prime.

%p A002808 := proc(n) option remember ; if n = 1 then 4; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) : fi; od: fi; end: A162738 := proc(n) A002808(n)*ceil( ithprime(n)/A002808(n)) ; end: seq(A162738(n),n=1..100) ; # _R. J. Mathar_, Jul 16 2009

%t prs=Prime[Range[60]];comps=Rest[Complement[Range[Last[prs]+1],prs]];Ceiling[First[#]/Last[#]]Last[#]&/@Thread[{prs,Take[comps,60]}] (* _Harvey P. Dale_, Oct 02 2011 *)

%K nonn

%O 1,1

%A _Leroy Quet_, Jul 12 2009

%E Extended beyond a(16) by _R. J. Mathar_, Jul 16 2009