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A194642 Units’ digits of the non-zero heptagonal numbers. 0
1, 7, 8, 4, 5, 1, 2, 8, 9, 5, 6, 2, 3, 9, 0, 6, 7, 3, 4, 0, 1, 7, 8, 4, 5, 1, 2, 8, 9, 5, 6, 2, 3, 9, 0, 6, 7, 3, 4, 0, 1, 7, 8, 4, 5, 1, 2, 8, 9, 5, 6, 2, 3, 9, 0, 6, 7, 3, 4, 0, 1, 7, 8, 4, 5, 1, 2, 8, 9, 5, 6, 2, 3, 9, 0, 6, 7, 3, 4, 0, 1, 7, 8, 4, 5, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

This is a periodic sequence with period 20 and cycle 1, 7, 8, 4, 5, 1, 2, 8, 9, 5, 6, 2, 3, 9, 0, 6, 7, 3, 4, 0.

LINKS

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

Index to sequences with linear recurrences with constant coefficients, signature (0,0,0,0,1,0,0,0,0,-1,0,0,0,0,1).

FORMULA

a(n)=a(n-20)

a(n)=a(n-5)-a(n-10)+a(n-15)

a(n)=45-a(n-1)-a(n-2)-a(n-3)-a(n-4)-a(n-10)-a(n-11)-a(n-12)-a(n-13)-a(n-14)

a(n)=90-a(n-1)-a(n-2)-a(n-3)-…-a(n-17)-a(n-18)-a(n-19)

a(n)=mod(1/2 n(5n-3),10)

G.f.: -x*(4*x^13 +3*x^12 +7*x^11 +6*x^10 +5*x^8 -5*x^6 +5*x^4 +4*x^3 +8*x^2 +7*x +1) / ((x -1)*(x^2 +1)*(x^4 +x^3 +x^2 +x +1)*(x^8 -x^6 +x^4 -x^2 +1)). - Colin Barker, Sep 23 2013

EXAMPLE

The seventh non-zero heptagonal number is A000566(7)=112, which has units’ digit 2. Hence a(7)=2.

MATHEMATICA

Table[Mod[n*(5*n-3)/2, 10], {n, 100}]

CROSSREFS

Cf. A000566.

Sequence in context: A220863 A197823 A011243 * A114857 A195340 A019794

Adjacent sequences:  A194639 A194640 A194641 * A194643 A194644 A194645

KEYWORD

nonn,easy,base

AUTHOR

Ant King, Aug 31 2011

STATUS

approved

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Last modified April 19 03:33 EDT 2014. Contains 240738 sequences.