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A194642 Units' digits of the nonzero 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 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) = 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) = (n*(5*n-3)/2) mod 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

a(n) = A010879(A000566(n)). - Michel Marcus, Aug 10 2015

EXAMPLE

The seventh nonzero 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, A010879.

Sequence in context: A220863 A197823 A011243 * A114857 A256920 A195340

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 August 31 23:57 EDT 2015. Contains 261257 sequences.