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 A066760 Sum_{1<=k<=n, k is not a divisor of n and k is not coprime to n} k. 5
 0, 0, 0, 0, 0, 4, 0, 6, 6, 18, 0, 27, 0, 40, 37, 42, 0, 79, 0, 89, 74, 108, 0, 145, 45, 154, 96, 183, 0, 274, 0, 210, 184, 270, 163, 360, 0, 340, 257, 411, 0, 556, 0, 467, 418, 504, 0, 669, 140, 683, 439, 657, 0, 880, 369, 805, 548, 810, 0, 1183, 0, 928, 779, 930, 502 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS This function can be used to prove no p^k is perfect or multi-perfect. LINKS Michael De Vlieger, Table of n, a(n) for n = 1..10000 FORMULA a(n) = 1 + n*(n+1)/2 - sigma(n) - n*phi(n)/2. a(n) = 0 if and only if n = 1, 4 or a prime. - Robert G. Wilson v, Jul 31 2004 EXAMPLE There are three integers that satisfy this definition for n = 12, namely 8, 9 and 10. These sum to 27, hence a(12) = 27. MAPLE f:= n -> 1 + n*(n+1)/2 - numtheory:-sigma(n) - n*numtheory:-phi(n)/2; 0, seq(f(n), n=2..100); # Robert Israel, Nov 02 2014 MATHEMATICA Table[n(n + 1)/2 + 1 - EulerPhi[n] * n/2 - DivisorSigma[1, n], {n, 2, 65}] (* Robert G. Wilson v, Jul 31 2004 *) Table[Sum[k * Boole[Not[Divisible[n, k]]] * Boole[GCD[n, k] > 1], {k, n - 1}], {n, 65}] (* Alonso del Arte, Nov 02 2014 *) PROG (PARI) a(n)=n*(n + 1 - eulerphi(n))\2 + 1 - sigma(n) \\ Charles R Greathouse IV, Nov 02 2014 (MAGMA) [0] cat [1 + n*(n+1)/2 - SumOfDivisors(n) - n*EulerPhi(n)/2: n in [2..70]]; // Vincenzo Librandi, Nov 03 2014 CROSSREFS Cf. A000010, A000203, A000217, A023896, A024816, A045763. Sequence in context: A133995 A019629 A073759 * A102393 A228131 A019833 Adjacent sequences:  A066757 A066758 A066759 * A066761 A066762 A066763 KEYWORD nonn,easy AUTHOR Jon Perry, Jan 17 2002 EXTENSIONS Offset corrected to 1 by Michael De Vlieger, Jul 05 2014 STATUS approved

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Last modified August 11 09:30 EDT 2020. Contains 336423 sequences. (Running on oeis4.)