A245779 Numbers n such that (n/tau(n) - sigma(n)/n) < 1.

1, 2, 3, 4, 6, 8, 10, 12, 18, 24

Offset

1,2

Comments

Numbers n such that A245776(n)/A245777(n) = n/A000005(n) - A000203(n)/n < 1.

Finite sequence with 10 terms.

Links

Table of n, a(n) for n=1..10.

Example

24 is in sequence because 24/tau(24) - sigma(24)/24 = 24/8 - 60/24 = 1/2.

Mathematica

a245779[n_Integer] :=
Select[Range[n],
  If[#/DivisorSigma[0, #] - DivisorSigma[1, #]/# < 1, True, False] &]; a245779[1000] (* Michael De Vlieger, Aug 07 2014 *)
Select[Range[25], #/DivisorSigma[0, #]-DivisorSigma[1, #]/#<1&] (* Harvey P. Dale, Nov 21 2023 *)

Prog

(Magma) [n:n in [1..1000000] | (Numerator((n /(#[d: d in Divisors(n)]))-(SumOfDivisors(n)/n))) / (Denominator((n/(#[d: d in Divisors(n)]))-(SumOfDivisors(n)/n))) lt 1]
(PARI)
for(n=1, 10^3, if(n/numdiv(n) - sigma(n)/n < 1, print1(n, ", "))) \\ Derek Orr, Aug 02 2014

Crossrefs

Cf. A000005, A000203, A245776, A245777, A245778, A245782.

Sequence in context: A216365 A034287 A067128 * A120432 A020490 A217660

Adjacent sequences: A245776 A245777 A245778 * A245780 A245781 A245782

Keyword

nonn,fini,full

Author

Jaroslav Krizek, Aug 02 2014

Status

approved