OFFSET
1,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000 (first 1000 terms from Reinhard Zumkeller)
Erich Friedman, What's Special About This Number? (See entry 34.)
FORMULA
MAPLE
q:= n-> is(nops(map(numtheory[tau], {$n-1..n+1}))=1):
select(q, [$1..3000])[]; # Alois P. Heinz, Jun 24 2021
MATHEMATICA
d[n_] := DivisorSigma[0, n];
samedQ[n_] := d[n-1] == d[n] == d[n+1];
Select[Range[3000], samedQ] (* Jean-François Alcover, Aug 01 2018 *)
1 + Flatten@Position[Differences@#&/@Partition[DivisorSigma[0, Range@3000], 3, 1], {0, 0}] (* Hans Rudolf Widmer, Feb 02 2023 *)
PROG
(Haskell)
a169834 n = a169834_list !! (n-1)
a169834_list = f a051950_list [0..] where
f (0:0:ws) (x:y:zs) = y : f (0:ws) (y:zs)
f (_:v:ws) (_:y:zs) = f (v:ws) (y:zs)
-- Reinhard Zumkeller, Aug 31 2014
(Python)
from sympy import divisor_count as d
def ok(n): return d(n-1) == d(n) == d(n+1)
print(list(filter(ok, range(1, 2400)))) # Michael S. Branicky, Jun 24 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 02 2010
STATUS
approved