A097515 a(n) = (largest prime < 10^n) + (smallest prime > 10^n).

18, 198, 2006, 19980, 199994, 1999986, 20000010, 199999996, 1999999944, 19999999986, 199999999980, 2000000000028, 20000000000008, 200000000000004, 2000000000000026, 19999999999999998, 200000000000000000, 1999999999999999992, 20000000000000000012, 200000000000000000028

Offset: 1

Author

Cino Hilliard, Aug 27 2004

Keywords

• nonn

Crossrefs

Cf. A003617, A003618.

Programs

Mathematica

Table[NextPrime[10^n,-1]+NextPrime[10^n],{n,20}] (* Harvey P. Dale, May 03 2018 *)

Formula

a(n) = A003618(n) + A003617(n+1). - Amiram Eldar, Jul 02 2024

Extensions

More terms from Amiram Eldar, Jul 02 2024