OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
d(10) = 4, d(11) = 2, and d(12) = 6. Now, (4,2,6) is a permutation of (2,4,6), which are three integers in arithmetic progression because 4-2 = 6-4. So 10 is included in the sequence.
MATHEMATICA
Position[Partition[DivisorSigma[0, Range[400]], 3, 1], _?(Length[Union[ Differences[ Sort[#]]]]==1&), 1, Heads->False]//Flatten (* Harvey P. Dale, Dec 09 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Feb 24 2010
EXTENSIONS
Extended by Ray Chandler, Mar 03 2010
STATUS
approved