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

%I A124450 #19 Aug 12 2025 03:29:23
%S A124450 5,47,491,4919,49877,499943,4999913,49999757,499999931,4999999937,
%T A124450 49999999811,499999999769,4999999998431,49999999999619,
%U A124450 499999999999769,4999999999998557,49999999999998887,499999999999999679,4999999999999999661,49999999999999998647
%N A124450 Lesser of a pair of not necessarily distinct closest primes that add up to 10^n.
%C A124450 a(n) is always an n digit number.
%C A124450 Note that if distinct primes are required, the only change is that a(1) = 3.
%H A124450 Hans Havermann, <a href="/A124450/b124450.txt">Table of n, a(n) for n = 1..50</a>
%F A124450 10^n - a(n) is prime.
%e A124450 10^1=5+5; 10^2=47+53; 10^3=491+509;
%e A124450 10^4=4919+5081; 10^5=49877=50123; 10^6=499943+500057;
%e A124450 10^7=4999913+5000087; 10^8=49999757+50000243;
%e A124450 10^9=499999931+500000069;
%e A124450 10^10=4999999937+5000000063; etc.
%t A124450 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 *)
%Y A124450 Cf. A065577 (number of Goldbach partitions of 10^n).
%Y A124450 Cf. A124013.
%K A124450 nonn
%O A124450 1,1
%A A124450 _Zak Seidov_, Nov 02 2006
%E A124450 Edited by _N. J. A. Sloane_ May 15 2008 at the suggestion of _R. J. Mathar_.