A163506 a(n) = n-th odd nonprime * n-th odd number.

1, 27, 75, 147, 225, 297, 429, 525, 663, 855, 1029, 1173, 1375, 1539, 1827, 2015, 2277, 2625, 2849, 3159, 3485, 3741, 4095, 4371, 4655, 5049, 5565, 6105, 6555, 6903, 7259, 7623, 7995, 8375, 8901, 9443, 9855, 10575, 11011, 11455, 11907, 12699, 13175, 13833

Offset: 1

Author

Juri-Stepan Gerasimov, Jul 29 2009

Keywords

• nonn

Examples

			a(1) =  1*1 =   1;
a(2) =  9*3 =  27;
a(3) = 15*5 =  75;
a(4) = 21*7 = 147;
a(5) = 25*9 = 225.
		

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A005408, A014076.

Programs

Maple

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:
A163506 := proc(n) A014076(n) *(2*n-1); end: seq(A163506(n),n=1..80) ; # R. J. Mathar, Oct 10 2009

Mathematica

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

Formula

a(n) = A014076(n)*A005408(n-1). - corrected by R. J. Mathar, Oct 10 2009

Extensions

7279 replaced with 7259 by R. J. Mathar, Oct 10 2009