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A217446
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Sum of the squares of numbers obtained by digit permutations of the concatenation of first n numbers.
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1
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1, 585, 331668, 213208980, 156226437720, 129158041750920, 119164964083502400, 121503028361696976960, 135757575541042424323200, 165013333307050666667644800, 216831999996550400000012812800, 306342399999513113600000180544000, 463124479999926454528000002723302400
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = (1/12)*(n+1)!*(n*R'(n)+(3*n+2)*R(n)^2) with R(n) = (10^n-1)/9 and R'(n) = (10^(2*n)-1)/99.
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EXAMPLE
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a(1) = 1^2 = 1.
a(2) = 12^2 + 21^2 = 585.
a(3) = 123^2 + 132^2 + 213^2 + 231^2 + 312^2 + 321^2 = 331668.
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MAPLE
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R:= n-> (10^n-1)/9: RP:= n-> (10^(2*n)-1)/99:
a:= n-> (1/12)*(n+1)!*(n*RP(n)+(3*n+2)*R(n)^2):
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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