OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..4000
Vaclav Kotesovec, Plot of a(n)/n for n = 1..1000000
Vaclav Kotesovec, Plot of a(n)/(n*log(log(n))) for n = 1..1000000
MATHEMATICA
Select[Range[1000], DivisorSigma[0, #]==DivisorSigma[0, #-1]+ DivisorSigma[ 0, #+1]&] (* Harvey P. Dale, Feb 27 2012 *)
Flatten[Position[Partition[DivisorSigma[0, Range[1000]], 3, 1], _?(#[[2]]==#[[1]]+#[[3]]&), 1, Heads->False]]+1 (* Much faster than the above Mathematica program because tau of each number only has to be calculated once. *) (* Harvey P. Dale, Jan 03 2020 *)
PROG
(PARI) is(n)=numdiv(n)==numdiv(n-1)+numdiv(n+1) \\ Charles R Greathouse IV, Apr 24 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Dec 05 2003
EXTENSIONS
More terms from Ray Chandler, Dec 09 2003
STATUS
approved