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Smallest nonprime number <= 10^n (n>=1) with maximum distance from a prime.
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%I #21 Feb 21 2019 09:20:55

%S 9,93,897,9569,31433,492170,4652430,47326803,436273150,4302407536,

%T 42652618575,738832928197,7177162612050,90874329411895,

%U 218209405436996,1693182318746937,80873624627235459,804212830686678390

%N Smallest nonprime number <= 10^n (n>=1) with maximum distance from a prime.

%C Each number is a mean of two consecutive primes.

%C Since, except 2, primes are odd numbers, this mean is an integer.

%e For n=1: first prime numbers are 2, 3, 5, 7 and 11. Maximum difference between two consecutive primes is 4 between 7 and 11 thus a(1)=9.

%e For n=4: maximum difference between two primes less than 10^4 is 36, which occurs once: between 9551 and 9587. a(4)=(9551 + 9587)/2 = 9569.

%Y Cf. A000040, A001223, A087378, A282690.

%K nonn,more

%O 1,1

%A _David Cobac_, Feb 18 2019

%E More terms (using the b-file at A002386) from _Jon E. Schoenfield_, Feb 19 2019