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A102040
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a(n) = a(n-1) + last digit of a(n-1), starting at 3.
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1
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3, 6, 12, 14, 18, 26, 32, 34, 38, 46, 52, 54, 58, 66, 72, 74, 78, 86, 92, 94, 98, 106, 112, 114, 118, 126, 132, 134, 138, 146, 152, 154, 158, 166, 172, 174, 178, 186, 192, 194, 198, 206, 212, 214, 218, 226, 232, 234, 238, 246, 252, 254, 258, 266, 272, 274, 278
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = -5-(1/2+i)*(-i)^n-(1/2-i)*i^n+5*n for n>1, where i = sqrt(-1).
a(n) = 2*a(n-1)-2*a(n-2)+2*a(n-3)-a(n-4) for n>5.
G.f.: x*(5*x^4-4*x^3+6*x^2+3) / ((x-1)^2*(x^2+1)).
(End)
a(n) = a(n-4) + 20 for n >= 6.
a(4k) = 20 k - 6.
a(4k+1) = 20 k - 2 for k >= 1.
a(4k+2) = 20 k + 6.
a(4k+3) = 20 k + 12. (End)
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EXAMPLE
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26+6=32, 32+2=34.
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MATHEMATICA
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a[1] = 3; a[n_] := a[n] = a[n - 1] + Last@ IntegerDigits@ a[n - 1]; Array[a, {57}] (* Michael De Vlieger, Oct 21 2015 *)
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PROG
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(PARI) a(n) = if(n==1, 3, -5-(1/2+I)*(-I)^n-(1/2-I)*I^n+5*n) \\ Colin Barker, Oct 21 2015
(PARI) Vec(x*(5*x^4-4*x^3+6*x^2+3)/((x-1)^2*(x^2+1)) + O(x^100)) \\ Colin Barker, Oct 21 2015
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CROSSREFS
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KEYWORD
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easy,nonn,base
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AUTHOR
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Samantha Stones (devilsdaughter2000(AT)hotmail.com), Dec 25 2004
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EXTENSIONS
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STATUS
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approved
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