A090178 a(1) = 2; for n > 1, a(n) = n + prime(n-1).

2, 4, 6, 9, 12, 17, 20, 25, 28, 33, 40, 43, 50, 55, 58, 63, 70, 77, 80, 87, 92, 95, 102, 107, 114, 123, 128, 131, 136, 139, 144, 159, 164, 171, 174, 185, 188, 195, 202, 207, 214, 221, 224, 235, 238, 243, 246, 259, 272, 277, 280, 285, 292, 295, 306, 313, 320, 327

Offset: 1

Author

Pab Ter (pabrlos(AT)yahoo.com), May 29 2004

Keywords

• nonn

Comments

Sum of index n and the corresponding n-th term of noncomposite numbers (A008578).

Does n > 2 exist such that n*prime(n-1)/(n+prime(n-1)), i.e., A164931(n)/a(n) is an integer? - Jaroslav Krizek, Aug 31 2009

Complement of A171508(n). - Jaroslav Krizek, Dec 13 2009

Examples

			a(2) = 2 + prime(1) = 4; a(5) = 5 + prime(4) = 12; a(9) = 9 + prime(8) = 28.
		

References

• M. Feenstra, P. J. Carter and C. P. Harding, The Ultimate I.Q. Book, Wardlock, see p. 99.

Crossrefs

The published version (A048171) is said to be incorrect.

Programs

Magma

[n + NthPrime(n-1): n in [1..58] ]; // Klaus Brockhaus, Sep 09 2009

Mathematica

Join[{2}, Table[Prime[n - 1] + n, {n, 2, 60}]] (* Vincenzo Librandi, Dec 08 2015 *)

Formula

a(n) = n + A008578(n). - David Wasserman, May 20 2008

a(1) = 2; a(n) = 1 + A014688(n-1), for n >= 2. - Omar E. Pol, Nov 01 2013

Extensions

Definition corrected, second comment and example edited by Klaus Brockhaus, Sep 09 2009