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A177930 a(n) is the smallest prime divisor of (A177929(n)-1)*(A177929(n)+1).

%I A177930 #10 May 13 2023 05:51:41
%S A177930 3,5,3,11,3,5,3,29,3,59,3,7,5,3,7,137,3,5,3,281,3,5,3,569,3,7,5,3,
%T A177930 1151,3,5,3,2309,3,31,4649,3,17,3,7,5,3,7,5,3,9341,3,5,3,11,3,59,3,29,
%U A177930 3,19,7,5,3,7,19,5,3,7,109,5,3,61,7,79,5,3,13,5,3,19139,3,101,3,7,13,11,3,71,3
%N A177930 a(n) is the smallest prime divisor of (A177929(n)-1)*(A177929(n)+1).
%C A177930 Records are in A177932, their positions in A177931.
%F A177930 a(n) = A020639( (A177929(n))^2 -1 ).
%t A177930 lpf[n_] := FactorInteger[n][[1, 1]];
%t A177930 b[n_] := b[n] = If[n == 1, 4, b[n-1]+lpf[b[n-1]^2-1]-1];
%t A177930 a[n_] := lpf[b[n]^2-1];
%t A177930 Table[a[n], {n, 1, 85}] (* _Jean-François Alcover_, May 13 2023 *)
%Y A177930 Cf. A001359, A020639, A177929, A174514, A174216, A174217
%K A177930 nonn
%O A177930 1,1
%A A177930 _Vladimir Shevelev_, May 15 2010
%E A177930 A 7 replaced by 17 and sequence extended by _R. J. Mathar_, May 31 2010