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A194886 Units' digits of the nonzero decagonal numbers. 0
1, 0, 7, 2, 5, 6, 5, 2, 7, 0, 1, 0, 7, 2, 5, 6, 5, 2, 7, 0, 1, 0, 7, 2, 5, 6, 5, 2, 7, 0, 1, 0, 7, 2, 5, 6, 5, 2, 7, 0, 1, 0, 7, 2, 5, 6, 5, 2, 7, 0, 1, 0, 7, 2, 5, 6, 5, 2, 7, 0, 1, 0, 7, 2, 5, 6, 5, 2, 7, 0, 1, 0, 7, 2, 5, 6, 5, 2, 7, 0, 1, 0, 7, 2, 5, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

This is a periodic sequence with period 10 and cycle 1,0,7,2,5,6,5,2,7,0.

LINKS

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

FORMULA

a(n) = a(n-10).

a(n) = 35 -a(n-1) -a(n-2) -a(n-3) -a(n-4) -a(n-5) -a(n-6) -a(n-7) -a(n-8) -a(n-9).

a(n) = mod(n(4n-3),10).

G.f.: x*(1 +7*x^2 +2*x^3 +5*x^4 +6*x^5 +5*x^6 +2*x^7 +7*x^8)/((1-x)*(1+x)*(1 +x +x^2 +x^3 +x^4)*(1 -x +x^2 -x^3 +x^4)).

a(n) = -n^2 + 2*n (mod 10). - Arkadiusz Wesolowski, Jul 03 2012

a(n) = A010879(A001107(n)). - Michel Marcus, Aug 10 2015

EXAMPLE

The seventh nonzero decagonal number is A001107(7)=175, which has units' digit 5. Hence a(7)=5.

MATHEMATICA

Table[Mod[n (4 n - 3), 10], {n, 86}]

PadRight[{}, 120, {1, 0, 7, 2, 5, 6, 5, 2, 7, 0}] (* Harvey P. Dale, Aug 17 2019 *)

CROSSREFS

Cf. A001107, A010879.

Sequence in context: A199080 A093072 A066903 * A196764 A074457 A200237

Adjacent sequences:  A194883 A194884 A194885 * A194887 A194888 A194889

KEYWORD

nonn,easy,base

AUTHOR

Ant King, Sep 07 2011

STATUS

approved

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Last modified April 9 04:05 EDT 2020. Contains 333343 sequences. (Running on oeis4.)