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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 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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