|
%I #16 Jun 10 2021 07:41:21
%S 1,3,3,213,213,1383,3091,8129,943607,943607,19235031,21470685,
%T 21470685,21470685,21470685
%N Least number that begins an n-term arithmetic progression with common difference 2 in which all terms have the same number of divisors.
%C Second column of A113465. Next term is > 6368300000.
%e a(4) = 213 because 213, 215, 217 and 219 each have 4 divisors.
%t 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 *)
%Y Cf. A113457, A113465.
%K nonn,less,hard
%O 1,2
%A _David Wasserman_, Jan 08 2006
|
