The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A343462

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A343462

Number of n-digit positive integers that undulate.
(history; published version)

#32 by Wesley Ivan Hurt at Wed Apr 28 12:54:30 EDT 2021

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editing

approved

#31 by Wesley Ivan Hurt at Wed Apr 28 12:54:23 EDT 2021

CROSSREFS

Cf. A057332. Apart from the first 2 terms , the same as A152464.

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proposed

editing

#30 by R. J. Mathar at Wed Apr 28 12:15:25 EDT 2021

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editing

proposed

#29 by R. J. Mathar at Wed Apr 28 12:15:21 EDT 2021

CROSSREFS

Cf. A057332. Apart from the first 2 terms the same as A152464.

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approved

editing

#28 by Michel Marcus at Sun Apr 25 02:33:42 EDT 2021

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reviewed

approved

#27 by Joerg Arndt at Sun Apr 25 01:29:13 EDT 2021

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proposed

reviewed

#26 by Chai Wah Wu at Sat Apr 24 22:19:35 EDT 2021

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editing

proposed

#25 by Chai Wah Wu at Sat Apr 24 22:18:59 EDT 2021

LINKS

<a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (5,10,-20,-15,21,7,-8,-1,1).

FORMULA

From Chai Wah Wu, Apr 24 2021: (Start)

a(n) = 5*a(n-1) + 10*a(n-2) - 20*a(n-3) - 15*a(n-4) + 21*a(n-5) + 7*a(n-6) - 8*a(n-7) - a(n-8) + a(n-9) for n > 10.

G.f.: x*(-8*x^9 + 7*x^8 + 63*x^7 - 45*x^6 - 162*x^5 + 81*x^4 + 150*x^3 - 30*x^2 - 36*x - 9)/(x^9 - x^8 - 8*x^7 + 7*x^6 + 21*x^5 - 15*x^4 - 20*x^3 + 10*x^2 + 5*x - 1). (End)

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approved

editing

#24 by N. J. A. Sloane at Sat Apr 24 21:38:35 EDT 2021

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proposed

approved

#23 by Jon E. Schoenfield at Sun Apr 18 00:15:33 EDT 2021

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editing

proposed

Discussion

Sun Apr 18

02:00

Kevin Ryde: A rough look suggests abab style (A046075) is more sequences "undulate".  On the other hand, A057333 is count primes in your style I think.  As long as defined eh.  I don't mind reckoning a single digit (or even no digits at all!), as obeying up down up down.  The count in A057333 includes single digits.