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A153789
First differences of harmonic (or Ore) numbers A001599.
1
5, 22, 112, 130, 226, 176, 966, 1332, 3230, 1928, 62, 10410, 20, 9226, 2394, 2520, 23100, 49804, 12136, 49600, 6200, 63910, 4550, 90580, 27720, 179040, 156120, 30660, 27300, 197496, 138294, 332010, 118440, 638820, 50960, 60760, 166740
OFFSET
1,1
LINKS
MATHEMATICA
a := Select[Range[1000000], IntegerQ[HarmonicMean[Divisors[#]]] &]; Table[Part[a, n + 1] - Part[a, n], {n, 1, 30}] (* G. C. Greubel, Aug 29 2016 *)
PROG
(GAP) H:=Concatenation([1], Filtered([2, 4..3*10^6], n->IsInt(n*Tau(n)/Sigma(n))));;
a:=List([1..Length(H)-1], i->H[i+1]-H[i]);; Print(a); # Muniru A Asiru, Dec 23 2018
(Python)
from numpy import diff
from sympy import divisor_sigma as sigma
def ore(n): return (n*sigma(n, 0))%sigma(n, 1) == 0
print(diff(list(filter(ore, range(1, 9000))))) # Michael S. Branicky, May 22 2021
CROSSREFS
Cf. A001599.
Sequence in context: A267241 A162271 A164593 * A213167 A355398 A005033
KEYWORD
nonn
AUTHOR
Omar E. Pol, Jan 20 2009
EXTENSIONS
More terms from R. J. Mathar, Feb 19 2009
STATUS
approved