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a(n) = tau(n)*(n-tau(n)), where tau(n) = number of divisors of n (A000005).
2

%I #27 Jul 27 2017 08:13:33

%S 0,0,2,3,6,8,10,16,18,24,18,36,22,40,44,55,30,72,34,84,68,72,42,128,

%T 66,88,92,132,54,176,58,156,116,120,124,243,70,136,140,256,78,272,82,

%U 228,234,168,90,380,138,264,188,276,102,368,204,384,212,216,114

%N a(n) = tau(n)*(n-tau(n)), where tau(n) = number of divisors of n (A000005).

%H Reinhard Zumkeller, <a href="/A076627/b076627.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A000005(n) * A049820(n). [_Reinhard Zumkeller_, Feb 06 2012]

%e a(20) = tau(20)*(20-tau(20)) = 6*(20-6) = 84.

%p with(numtheory): A076627:=n->tau(n)*(n-tau(n)): seq(A076627(n), n=1..100); # _Wesley Ivan Hurt_, Jul 25 2017

%t #[[1]](#[[2]]-#[[1]])&/@Table[{DivisorSigma[0,n],n},{n,60}] (* _Harvey P. Dale_, May 06 2017 *)

%o (Haskell)

%o a076627 n = a000005 n * a049820 n -- _Reinhard Zumkeller_, Feb 06 2012

%o (PARI) a(n) = my(d = numdiv(n)); d*(n-d); \\ _Michel Marcus_, Jul 25 2017

%Y Cf. A000005, A049820.

%K nonn,easy

%O 1,3

%A _Reinhard Zumkeller_, May 27 2003

%E Wrong offset fixed by _Reinhard Zumkeller_, Feb 06 2012