login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A064385 a(n) = 2*5^n - 3. 1
7, 47, 247, 1247, 6247, 31247, 156247, 781247, 3906247, 19531247, 97656247, 488281247, 2441406247, 12207031247, 61035156247, 305175781247, 1525878906247, 7629394531247, 38146972656247 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

5th polygonal numbers for polygons of 5^n sides divided by 5: p(5,5^x)/5, where p(n,k) = (n/2)*(n*k - k + 4 - 2*n).

This sequence exhibits periodic digit repetition; e.g. the last digit repeats as 7, the penultimate as 4 and the antepenultimate as 2, all with a period of 1; the fourth-to-last digit repeats the sequence 1, 6 with a period of 2; the fifth-to-last repeats the sequence 3, 5, 8, 0; the sixth-to-last repeats 1, 7, 9, 5, 6, 2, 4, 0. And so on, it seems, for the other digits as the numbers grow.

LINKS

Harry J. Smith, Table of n, a(n) for n=1,...,100

Index entries for linear recurrences with constant coefficients, signature (6,-5).

FORMULA

From Vincenzo Librandi, Nov 12 2011: (Start)

a(n) = 5*a(n-1) + 12.

a(n) = 6*a(n-1) - 5*a(n-2).

G.f.: (2 - 5*x + 15*x^2)/((1-x)*(1-5*x)).

(End)

MAPLE

p := proc(n, k) (n/2)*(n*k-k+4-2*n) end: for x from 1 to 19 do p(5, 5^x)/5 od; q := proc(x) 2*5^x-3 end: for x from 1 to 19 do q(x) od;

PROG

(PARI) p(n, k) = (n/2)*(n*k-k+4-2*n) for(x=1, 19, print(p(5, 5^x)/5)) q(x) = 2*5^x-3 for(x=1, 19, print(q(x)))

(PARI) { for (n=1, 100, write("b064385.txt", n, " ", 2*5^n - 3) ) } \\ Harry J. Smith, Sep 13 2009

(MAGMA) [2*5^n-3: n in [1..30]]; // Vincenzo Librandi, Nov 12 2011

CROSSREFS

Sequence in context: A009202 A093112 A091516 * A269520 A009260 A201871

Adjacent sequences:  A064382 A064383 A064384 * A064386 A064387 A064388

KEYWORD

nonn,easy

AUTHOR

Daniel Dockery (drd(AT)peritus.virtualave.net), Sep 16 2001

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 13 19:25 EST 2018. Contains 317149 sequences. (Running on oeis4.)