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A161462 Final digit of sum of all the natural numbers from n to 2*n-1. 0
1, 5, 2, 2, 5, 1, 0, 2, 7, 5, 6, 0, 7, 7, 0, 6, 5, 7, 2, 0, 1, 5, 2, 2, 5, 1, 0, 2, 7, 5, 6, 0, 7, 7, 0, 6, 5, 7, 2, 0, 1, 5, 2, 2, 5, 1, 0, 2, 7, 5, 6, 0, 7, 7, 0, 6, 5, 7, 2, 0, 1, 5, 2, 2, 5, 1, 0, 2, 7, 5, 6, 0, 7, 7, 0, 6, 5, 7, 2, 0, 1, 5, 2, 2, 5, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Periodic with period length 20. - R. J. Mathar, May 21 2010

Also, units digits of the pentagonal numbers. - Ant King, Jul 12 2011

LINKS

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

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

FORMULA

a(n) = A000326(n) mod 10. a(n)= +a(n-5) -a(n-10) +a(n-15). [From R. J. Mathar, May 21 2010]

a(n)=a(n-20) (Ant King, Jul 12 2011)

a(n)=70-a(n-1)-a(n-2)-a(n-3)-....-a(n-19) [Ant King, Jul 12 2011]

EXAMPLE

If n=1, then a(1)=1. If n=2 and 2+3=5, then a(2)=5. if n=3 and 3+4+5=12, then a(3)=2, etc.

MATHEMATICA

Table[Mod[n*(3*n - 1)/2, 10], {n, 100}] (* Ant King, Jul 12 2011 *)

CROSSREFS

Cf. A000027, A000326.

Sequence in context: A198496 A318332 A177925 * A259649 A217868 A153842

Adjacent sequences:  A161459 A161460 A161461 * A161463 A161464 A161465

KEYWORD

nonn,base,easy

AUTHOR

Juri-Stepan Gerasimov, Jun 10 2009

EXTENSIONS

Entries confirmed by R. J. Mathar, May 21 2010

STATUS

approved

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Last modified July 5 03:37 EDT 2020. Contains 335459 sequences. (Running on oeis4.)