A137507 a(n) = 100^[n/10] + 2*n*10^[n/10]: inspired by Engel expansion of Pi.

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 14000, 14200, 14400, 14600, 14800, 15000, 15200, 15400, 15600, 15800, 1060000, 1062000, 1064000, 1066000, 1068000, 1070000, 1072000, 1074000, 1076000, 1078000, 100800000, 100820000

Offset: 0

Author

Alexander R. Povolotsky, Apr 23 2008

Keywords

• nonn
• easy

Links

• G. C. Greubel, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,0,0,0,0,0,120,0,0,0,0,0,0,0,0,0,-2100,0,0,0,0,0,0,0,0,0,10000).

Crossrefs

Cf. A006784.

Programs

Mathematica

Table[100^(Floor[n/10]) + 2*n*10^(Floor[n/10]), {n,0,50}] (* G. C. Greubel, Feb 23 2017 *)

PARI

a(n) = (n + 10^(floor(n/10)))^2 - n^2;

PARI

vector(30,n, n--; 2*n*10^(n\10) + 100^(n\10)) \\ M. F. Hasler, May 02 2008

Sage

[(n + 10^(floor(n/10)))^2 - n^2 for n in range(0,42)] # Stefano Spezia, Apr 16 2025

Extensions

Edited by M. F. Hasler and N. J. A. Sloane, May 02 2008