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

 

Logo

The submissions stack has been unacceptably high for several months now. Please voluntarily restrict your submissions and please help with the editing. (We don't want to have to impose further limits.)

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A205651 Period 6: repeat (1, 6, 5, 4, 9, 0). 0
1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6, 5, 4, 9, 0, 1, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The members of this sequence are also the units' digits of the indices of those nonzero square numbers that are also triangular.

The coefficients of x^n in the numerator of the generating function form the periodic cycle of the sequence.

LINKS

Table of n, a(n) for n=1..86.

Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,0,1).

FORMULA

G.f. x*(1+6*x+5*x^2+4*x^3+9*x^4) / ((1-x)*(1+x)*(1-x+x^2)*(1+x+x^2)).

a(n) = a(n-6).

a(n) = 25-a(n-1)-a(n-2)-a(n-3)-a(n-4)-a(n-5).

For n>0, a(n) = A010879(A001109(n)) = A010879(sqrt(A001110(n))) = mod(A001109(n),10).

EXAMPLE

The fourth nonzero square number that is also a triangular number is 204^2. As 204 has units' digit 4, then a(4)=4.

MATHEMATICA

LinearRecurrence[{0, 0, 0, 0, 0, 1}, {1, 6, 5, 4, 9, 0}, 86]

PROG

(PARI) a(n)=[0, 1, 6, 5, 4, 9][n%6+1] \\ Charles R Greathouse IV, Jan 31 2012

CROSSREFS

Cf. A010879, A001109, A001110.

Sequence in context: A200096 A220086 A094773 * A168239 A019131 A019132

Adjacent sequences:  A205648 A205649 A205650 * A205652 A205653 A205654

KEYWORD

nonn,easy

AUTHOR

Ant King, Jan 31 2012

STATUS

approved

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

Content is available under The OEIS End-User License Agreement .

Last modified August 29 10:37 EDT 2015. Contains 261188 sequences.