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a(n) is the least prime factor of (9 * 10^(6*n-4) - 11) / 7.
1

%I #8 May 25 2024 21:06:19

%S 127,401,19,53,151,7,139,127,19,78721,3458771,19,7,38954263,19,79,53,

%T 19,157,7,19,127,18191,19,12119,421,7,

%U 107434435760557861791327959267859939351202240879711219728393537522815146155523913,79,19,23196834569628410341642097660316821

%N a(n) is the least prime factor of (9 * 10^(6*n-4) - 11) / 7.

%H Sean A. Irvine, <a href="/A122691/b122691.txt">Table of n, a(n) for n = 1..69</a>

%e n=2, (9*10^8-11)/7 = 128571427 = 401 * 320627 hence a(2)=401.

%Y Cf. A100275, A122862.

%K nonn

%O 1,1

%A _Zak Seidov_, Sep 22 2006

%E a(28) onward corrected by _Sean A. Irvine_, May 25 2024