A175149 A positive integer n is included if (d(n),d(n+1),d(n+2)) is a permutation of three integers in arithmetic progression, where d(n) = the number of divisors of n.

4, 7, 9, 10, 12, 19, 27, 31, 33, 45, 51, 61, 67, 68, 73, 76, 85, 93, 114, 141, 153, 154, 162, 164, 174, 186, 187, 190, 201, 208, 211, 213, 217, 220, 230, 236, 242, 243, 245, 258, 261, 266, 267, 273, 277, 290, 291, 294, 301, 308, 337, 342, 354, 355, 356, 364, 367

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

Cf. A000005.

Sequence in context: A287678 A335229 A310939 * A153053 A045752 A266410

Adjacent sequences: A175146 A175147 A175148 * A175150 A175151 A175152

Keyword

nonn

Author

Leroy Quet, Feb 24 2010

Extensions

Extended by Ray Chandler, Mar 03 2010

Status

approved