A221945 a(n) = floor(sqrt(2*5^n)).

1, 3, 7, 15, 35, 79, 176, 395, 883, 1976, 4419, 9882, 22097, 49410, 110485, 247052, 552427, 1235264, 2762135, 6176323, 13810679, 30881617, 69053396, 154408088, 345266983, 772040444, 1726334915, 3860202221, 8631674575, 19301011109, 43158372875, 96505055547, 215791864375, 482525277735

Offset: 0

Author

N. J. A. Sloane, Feb 01 2013

Keywords

• nonn

Comments

Floor of norm of (1 + i) * (1 + 2i)^n. - Jon Perry, Dec 06 2013

Links

• G. C. Greubel, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A017910, A017913, A017919, A114183, A221718, A221942-A221946.

Programs

Magma

[Floor(Sqrt(2*5^n)): n in [0..40]]; // G. C. Greubel, Oct 06 2018

Mathematica

Table[Floor[Sqrt[2*5^n]],{n,0,40}] (* Harvey P. Dale, Feb 10 2016 *)

PARI

a(n)=sqrtint(2*5^n) \\ Charles R Greathouse IV, Apr 18 2013