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A290703 Solutions to x + d(x) = sigma(x)/2, where d(x) is the number of divisors of x.

%I A290703 #15 Aug 30 2017 21:45:35
%S A290703 176,2205,7544,10184,28544,503296,1020568,2051072,6019264,10001848,
%T A290703 15317696,35019968,354375344,535871488,9175990784,115917884416
%N A290703 Solutions to x + d(x) = sigma(x)/2, where d(x) is the number of divisors of x.
%e A290703 d(176) = 10, sigma(176) = 372 and 176 + 10 = 186 = 372/2.
%p A290703 with(numtheory): P:=proc(q) local n; for n from 1 to q do if
%p A290703 n+tau(n)=sigma(n)/2 then print(n); fi; od; end: P(10^9);
%t A290703 Select[Range[10^7], # + DivisorSigma[0, #] == DivisorSigma[1, #]/2 &] (* _Michael De Vlieger_, Aug 26 2017 *)
%o A290703 (PARI) isok(x) = x + numdiv(x) == sigma(x)/2; \\ _Michel Marcus_, Aug 25 2017
%Y A290703 Cf. A000005, A099650, A111592, A290704.
%K A290703 nonn,more
%O A290703 1,1
%A A290703 _Paolo P. Lava_, Aug 09 2017
%E A290703 a(11)-a(12) from _Michel Marcus_, Aug 25 2017
%E A290703 a(13)-a(16) from _Giovanni Resta_, Aug 25 2017