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A190876 Numbers 1 through 8 together with numbers congruent to 9 mod 10. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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

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Last modified July 30 07:38 EDT 2021. Contains 346348 sequences. (Running on oeis4.)