OFFSET
1,2
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Bruno Berselli)
Marco Abrate, Stefano Barbero, Umberto Cerruti, Nadir Murru, The Biharmonic mean, arXiv:1601.03081 [math.NT], 2016, pages 6-14.
Umberto Cerruti, Numeri Armonici e Numeri Perfetti (in Italian), 2013. The sequence is on page 13.
MAPLE
with(numtheory); P:=proc(q) local a, k, n;
for n from 1 to q do a:=divisors(n);
if type((n*tau(n)+add(a[k]^2, k=1..nops(a)))/(2*sigma(n)), integer) then print(n); fi; od; end; P(1000); # Paolo P. Lava, Oct 11 2013
MATHEMATICA
B[n_] := (n DivisorSigma[0, n] + DivisorSigma[2, n])/(2 DivisorSigma[1, n]); Select[Range[300], IntegerQ[B[#]] &]
PROG
(Magma) IsInteger := func<i | i eq Floor(i)>; [n: n in [1..300] | IsInteger((n*NumberOfDivisors(n)+DivisorSigma(2, n))/(2*SumOfDivisors(n)))];
(Haskell)
a210494 n = a210494_list !! (n-1)
a210494_list = filter
(\x -> (a001157 x + a038040 x) `mod` a074400 x == 0) [1..]
-- Reinhard Zumkeller, Jan 21 2014
(PARI) isok(n) = denominator((n*sigma(n, 0) + sigma(n, 2))/(2*sigma(n)))==1; \\ Michel Marcus, Jan 14 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Bruno Berselli, Oct 03 2013 - proposed by Umberto Cerruti (Department of Mathematics "Giuseppe Peano", University of Turin, Italy)
STATUS
approved