A065856 The (2^n)-th composite number.

4, 6, 9, 15, 26, 48, 88, 168, 323, 627, 1225, 2406, 4736, 9351, 18504, 36655, 72730, 144450, 287147, 571208, 1136971, 2264215, 4510963, 8990492, 17923944, 35743996, 71298762, 142249762, 283859985, 566537515, 1130886504, 2257704401, 4507834166, 9001524190

Offset: 0

Author

Labos Elemer, Nov 26 2001

Keywords

• nonn

Comments

a(n) = A002808(A000079(n)).

Examples

			composite[1] = composite[2^0] = 4, composite[2] = composite[2^1] = 6, composite[1024] = composite[2^10] = 1225, composite[1073741824] = composite[2^30] = 1130886504.
		

Links

• Chai Wah Wu, Table of n, a(n) for n = 0..70

Crossrefs

Cf. A033844, A002808, A062298, A000720, A065855.

Programs

Mathematica

Composite[n_Integer] := Block[ {k = n + PrimePi[n] + 1 }, While[ k != n + PrimePi[k] + 1, k = n + PrimePi[k] + 1]; Return[ k ]]; Table[ Composite[2^n], {n, 0, 36} ]

Formula

a(n)-pi(a(n))-1 = 2^n.

Extensions

More terms from Robert G. Wilson v, Nov 26 2001

Definition corrected by N. J. A. Sloane, Jun 07 2009

Further corrections from Reinhard Zumkeller, Jun 24 2009

a(32)-a(33) from Chai Wah Wu, Apr 16 2018