|
%I #10 Feb 12 2020 20:13:04
%S 0,2,12,24,36,45,60,84,105,120,144,180,210,231,264,300,325,351,378,
%T 420,480,528,561,595,630,684,741,780,840,924,990,1035,1104,1176,1225,
%U 1275,1326,1404,1485,1540,1596,1653,1740,1860,1953,2016,2080,2145,2244,2346
%N a(n) = nonprime(n)*nonprime(n+1)/2, where nonprime(n) = A141468(n).
%e a(1) = 0*1/2 = 0, a(2) = 1*4/2 = 2, a(3) = 4*6/2 = 12, etc.
%p A141468 := proc(n) option remember ; local a; if n = 1 then 0; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: A144551 := proc(n) A141468(n)*A141468(n+1)/2 ; end: for n from 1 to 200 do printf("%d,",A144551(n)) ; od: # _R. J. Mathar_, Jan 03 2009
%t (Times@@#)/2&/@Partition[Select[Range[0,100],!PrimeQ[#]&],2,1] (* _Harvey P. Dale_, Feb 12 2020 *)
%o (PARI) c(n) = {for(k=0, primepi(n), isprime(n++)&&k--); n};
%o t(n) = if(n<3,n-1,c(n-2));
%o vector(100, n, t(n)*t(n+1)/2) \\ _Altug Alkan_, Oct 17 2015
%Y Cf. A141468.
%K nonn
%O 1,2
%A _Juri-Stepan Gerasimov_, Dec 31 2008
%E 1963 replaced by 1953 by _R. J. Mathar_, Jan 03 2009
|
