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A008954
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Final digit of triangular number n*(n+1)/2.
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8
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0, 1, 3, 6, 0, 5, 1, 8, 6, 5, 5, 6, 8, 1, 5, 0, 6, 3, 1, 0, 0, 1, 3, 6, 0, 5, 1, 8, 6, 5, 5, 6, 8, 1, 5, 0, 6, 3, 1, 0, 0, 1, 3, 6, 0, 5, 1, 8, 6, 5, 5, 6, 8, 1, 5, 0, 6, 3, 1, 0, 0, 1, 3, 6, 0, 5, 1, 8, 6, 5, 5, 6, 8, 1, 5, 0, 6, 3, 1, 0, 0, 1, 3, 6, 0, 5, 1, 8, 6, 5, 5, 6, 8, 1, 5, 0, 6, 3, 1, 0
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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LINKS
| Index entries for sequences related to final digits of numbers
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FORMULA
| a(1) = 1, a(n+1) = (a(n) + n + 1) mod 10.
Periodic with period 20: repeat [0,1,3,6,0,5,1,8,6,5,5,6,8,1,5,0,6,3,1,0]. - Frank Adams-Watters (FrankTAW(AT)Netscape.net), Mar 13 2006
a(n) = n(n+1)/2 mod 10 [From Ant King, April 26 2009].
a(n) = a(n-5) - a(n-10) + a(n-15). G.f.: -(x^12+3*x^11+6*x^10+5*x^8+5*x^6+5*x^4+6*x^2+3*x+1)*x / ( (x-1)*(x^2+1)*(x^4+x^3+x^2+x+1)*(x^8-x^6+x^4-x^2+1) ). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 15 2010]
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MATHEMATICA
| Table[ Mod[ n*(n + 1)/2, 10 ], {n, 0, 80} ]
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CROSSREFS
| Cf. A000217, A061501.
Cf. A008953. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), May 12 2010]
Sequence in context: A113565 A178567 A038023 * A169890 A141703 A021739
Adjacent sequences: A008951 A008952 A008953 * A008955 A008956 A008957
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KEYWORD
| nonn,base,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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