A124450 Lesser of a pair of not necessarily distinct closest primes that add up to 10^n.

5, 47, 491, 4919, 49877, 499943, 4999913, 49999757, 499999931, 4999999937, 49999999811, 499999999769, 4999999998431, 49999999999619, 499999999999769, 4999999999998557, 49999999999998887, 499999999999999679, 4999999999999999661, 49999999999999998647

Offset: 1

Author

Zak Seidov, Nov 02 2006

Keywords

• nonn

Comments

a(n) is always an n digit number.

Note that if distinct primes are required, the only change is that a(1) = 3.

Examples

			10^1=5+5; 10^2=47+53; 10^3=491+509;
10^4=4919+5081; 10^5=49877=50123; 10^6=499943+500057;
10^7=4999913+5000087; 10^8=49999757+50000243;
10^9=499999931+500000069;
10^10=4999999937+5000000063; etc.
		

Links

• Hans Havermann, Table of n, a(n) for n = 1..50

Crossrefs

Cf. A065577 (number of Goldbach partitions of 10^n).

Cf. A124013.

Programs

Mathematica

Table[ h =10^n/2; c=0; While[ PrimeQ[ h-c ]==False || PrimeQ[ h+c ]==False, c++ ]; h-c, {n, 1, 50} ] (* Hans Havermann, Nov 02 2006 *)

Formula

10^n - a(n) is prime.

Extensions

Edited by N. J. A. Sloane May 15 2008 at the suggestion of R. J. Mathar.