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%I #29 Nov 15 2022 02:37:17
%S 1,3,5,7,3,11,13,3,17,19,3,23,5,3,29,31,3,5,37,3,41,43,3,47,7,3,53,5,
%T 3,59,61,3,5,67,3,71,73,3,7,79,3,83,5,3,89,7,3,5,97,3,101,103,3,107,
%U 109,3,113,5,3,7,11,3,5,127,3,131,7,3,137,139,3,11,5,3,149,151,3,5,157,3,7
%N a(1) = 1; for n > 1, smallest divisor > 1 of 2n-1.
%C For n > 1, a(n) is an odd prime. - _Chai Wah Wu_, Nov 14 2022
%H Remi Eismann, <a href="/A090368/b090368.txt">Table of n, a(n) for n = 1..10000</a>
%t Join[{1},Divisors[#][[2]]&/@Range[3,161,2]] (* _Harvey P. Dale_, Oct 09 2011 *)
%t a[n_] := FactorInteger[2*n-1][[1,1]]; Array[a, 80] (* _Amiram Eldar_, Jun 11 2022 *)
%o (PARI) a(n)=if(n>1, factor(2*n-1)[1,1], 1) \\ _Charles R Greathouse IV_, Nov 09 2016
%o (Python)
%o from sympy import primefactors
%o def A090368(n): return min(primefactors((n<<1)-1), default=1) # _Chai Wah Wu_, Nov 14 2022
%Y Bisection of A020639.
%Y Cf. A100773.
%K nonn
%O 1,2
%A _Lekraj Beedassy_, Nov 27 2003
%E More terms from _Ray Chandler_, Dec 02 2003
%E Definition corrected by _Rémi Eismann_, May 08 2007
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