A190876 Numbers 1 through 8 together with numbers congruent to 9 mod 10.

1, 2, 3, 4, 5, 6, 7, 8, 9, 19, 29, 39, 49, 59, 69, 79, 89, 99, 109, 119, 129, 139, 149, 159, 169, 179, 189, 199, 209, 219, 229, 239, 249, 259, 269, 279, 289, 299, 309, 319, 329, 339, 349, 359, 369, 379, 389, 399, 409, 419, 429, 439, 449, 459, 469, 479, 489, 499, 509, 519, 529, 539, 549, 559, 569, 579, 589, 599, 609

Offset

1,2

Comments

In lunar arithmetic, numbers n with the property that the sum of the divisors of n that are <= n is equal to n.

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

D. Applegate, M. LeBrun and N. J. A. Sloane, Dismal Arithmetic [Note: we have now changed the name from "dismal arithmetic" to "lunar arithmetic" - the old name was too depressing]

Index entries for sequences related to dismal (or lunar) arithmetic

Index entries for linear recurrences with constant coefficients, signature (2,-1).

Formula

G.f.: x*(1+9*x^9)/(1-x)^2. - Bruno Berselli, May 23 2011

a(n) = 2*a(n-1) -a(n-2). - Vincenzo Librandi, Jul 12 2012

Prog

(Maxima) makelist(if n<9 then n else 10*n-81, n, 1, 70); /* Bruno Berselli, May 24 2011 */
(Magma) [n lt 9 select n else 10*n-81: n in [1..70]]; // Bruno Berselli, May 24 2011

Crossrefs

Cf. A017377.

Sequence in context: A088473 A317110 A340254 * A051885 A227378 A226637

Adjacent sequences: A190873 A190874 A190875 * A190877 A190878 A190879

Keyword

nonn,base

Author

N. J. A. Sloane, May 23 2011

Status

approved