A163506 - OEIS

%I #14 May 05 2019 00:36:41

%S 1,27,75,147,225,297,429,525,663,855,1029,1173,1375,1539,1827,2015,

%T 2277,2625,2849,3159,3485,3741,4095,4371,4655,5049,5565,6105,6555,

%U 6903,7259,7623,7995,8375,8901,9443,9855,10575,11011,11455,11907,12699,13175,13833

%N a(n) = n-th odd nonprime * n-th odd number.

%H G. C. Greubel, <a href="/A163506/b163506.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A014076(n)*A005408(n-1). - corrected by _R. J. Mathar_, Oct 10 2009

%e a(1) =  1*1 =   1;

%e a(2) =  9*3 =  27;

%e a(3) = 15*5 =  75;

%e a(4) = 21*7 = 147;

%e a(5) = 25*9 = 225.

%p A014076 := proc(n) option remember; local a; if n = 1 then 1; else for a from procname(n-1)+2 by 2 do if not isprime(a) then return a; end if; end do: end if; end proc:

%p A163506 := proc(n) A014076(n) *(2*n-1); end: seq(A163506(n),n=1..80) ; # _R. J. Mathar_, Oct 10 2009

%t A014076 := Select[Range[1, 10000, 2], PrimeOmega[#] != 1 &]; Table[A014076[[n]]*(2*n - 1), {n, 1, 50}] (* _G. C. Greubel_, Jul 27 2017 *)

%Y Cf. A005408, A014076.

%K nonn

%O 1,2

%A _Juri-Stepan Gerasimov_, Jul 29 2009

%E 7279 replaced with 7259 by _R. J. Mathar_, Oct 10 2009