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A022958 a(n) = 2 - n. 20
2, 1, 0, -1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16, -17, -18, -19, -20, -21, -22, -23, -24, -25, -26, -27, -28, -29, -30, -31, -32, -33, -34, -35, -36, -37, -38, -39, -40, -41, -42, -43, -44, -45, -46, -47, -48, -49, -50, -51, -52, -53, -54, -55 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,1
COMMENTS
a(n) is the Euler characteristic of one-sided surface of genus n (see Courant and Herbert). - Stefano Spezia, Sep 10 2022
LINKS
Richard Courant and Herbert Robbins, What Is Mathematics?, Oxford, 1941, p. 262.
Tanya Khovanova, Recursive Sequences
FORMULA
From Paul Barry, Mar 31 2007: (Start)
G.f.: (2-3x)/(1-x)^2.
E.g.f.: exp(x)*(2-x). (End)
a(n) = 2*a(n-1) - a(n-2); a(0)=2, a(1)=1. - Philippe Deléham, Nov 03 2008
MATHEMATICA
2-Range[0, 60] (* or *) LinearRecurrence[{2, -1}, {2, 1}, 60] (* Harvey P. Dale, Feb 23 2023 *)
PROG
(PARI) a(n)=n-2 \\ Charles R Greathouse IV, Jun 11 2015
CROSSREFS
Cf. A239229.
Sequence in context: A297158 A065358 A062329 * A023444 A248157 A290428
KEYWORD
sign,easy
AUTHOR
STATUS
approved

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Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)