A113466 Least number that begins an n-term arithmetic progression with common difference 2 in which all terms have the same number of divisors.

1, 3, 3, 213, 213, 1383, 3091, 8129, 943607, 943607, 19235031, 21470685, 21470685, 21470685, 21470685

Offset

1,2

Comments

Second column of A113465. Next term is > 6368300000.

Links

Table of n, a(n) for n=1..15.

Example

a(4) = 213 because 213, 215, 217 and 219 each have 4 divisors.

Mathematica

Module[{nn=21470695, ds}, ds=Table[DivisorSigma[0, n], {n, 1, nn, 2}]; 2*Table[ SequencePosition[ds, PadRight[{}, k, x_], 1], {k, 15}][[All, 1]]][[All, 1]]-1 (* Requires Mathematica version 10 or later *) (* The program will take a long time to run. To generate the first 8 terms of the sequence, change the nn constant to 8200 and the k range from 15 to 8 and the program will run quickly. *) (* Harvey P. Dale, Aug 16 2020 *)

Crossrefs

Cf. A113457, A113465.

Sequence in context: A152418 A273925 A113457 * A007301 A009715 A344283

Adjacent sequences: A113463 A113464 A113465 * A113467 A113468 A113469

Keyword

nonn,less,hard

Author

David Wasserman, Jan 08 2006

Status

approved