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a(n) = (A179017(n)+1)/2.
2

%I #19 Mar 23 2020 04:05:00

%S 2,3,6,7,11,15,22,30,31,34,35,39,42,43,47,58,62,66,67,70,71,78,79,83,

%T 87,94,102,103,106,107,110,111,114,115,119,130,134,139,142,143,146,

%U 155,159,166,174,178,179,183,186,187,191,195,202,206,210,211,214,215,218,219

%N a(n) = (A179017(n)+1)/2.

%C For numbers a and c, see A172186 and A179017. Numbers b are this sequence.

%C These numbers c, with distribution a+b=c such that a=(c-1)/2 and b=(c+1)/2, have minimal possible values with function L(a,b,c) = log(c)/log(N[a,b,c]) = log(c)/log((c^2-1)c/4).

%C There exist no numbers or distributions for which L < log(c)/log((c^2-1)c/4). - _Artur Jasinski_

%H Amiram Eldar, <a href="/A179019/b179019.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A179017(n) - A172186(n). - _Hugo Pfoertner_, Mar 22 2020

%t aa = {}; Do[If[(GCD[x, (x - 1)/2] == 1) && (GCD[x, (x + 1)/2] == 1) && (GCD[(x - 1)/2, (x + 1)/2] == 1), If[SquareFreeQ[(x^2 - 1) x/4], AppendTo[aa, (x + 1)/2]]], {x, 2, 1000}]; aa

%Y Cf. A172120, A172121, A147298, A147299, A147300, A147301, A147302, A147306, A147307, A147638, A147639, A147640, A147641, A147642, A147643, A143700, A179017, A172186.

%K nonn

%O 1,1

%A _Artur Jasinski_, Jun 24 2010