cp's OEIS Frontend

A124050 Difference between (first Chen prime > 10^n) and 10^n.

%I A124050 #6 Dec 24 2015 02:40:41
%S A124050 1,1,1,9,7,19,37,19,7,7,19,19,61,687,97,91,79,13,79,97,151,217,427,
%T A124050 253,667,13,127,427,457,577,1069,349,1147,1267,2527,2833,709,871,259,
%U A124050 361,1651,391,2689,649,31,3007,1657,2257,3757,5977,1441,2779,5749,367,31
%N A124050 Difference between (first Chen prime > 10^n) and 10^n.
%C A124050 A033873(n) <= a(n) <= A124001(n) and a(n) = A033873(n) for n = 0, 1, 2, 3, 4, 7, 8, 9, 10, 25, 44, 54.
%e A124050 a(0) = 1 because 2 is prime, 2 + 2 = 4 semiprime and 2 - 10^0 = 1,
%e A124050 a(1) = 1 because 11 and 13 are twin primes and 11 - 10^1 = 1,
%e A124050 a(2) = 1 because 101 and 103 are twin primes and 101 - 10^2 = 1,
%e A124050 a(3) = 9 because 1009 is prime, 1011 = 3*337 semiprime and 1009 - 10^3 = 9,
%e A124050 a(4) = 7 because 10007 and 10009 are twin primes and 10007 - 10^4 = 7,
%e A124050 a(5) = 19 because 100019 is prime, 100021 = 29*3449 semiprime and 100019 - 10^5 = 19, etc.
%Y A124050 Cf. A033873, A109611, A124001.
%K A124050 nonn
%O A124050 0,4
%A A124050 _Zak Seidov_, Nov 03 2006