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A274535
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a(n) = 5*sigma(n).
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16
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5, 15, 20, 35, 30, 60, 40, 75, 65, 90, 60, 140, 70, 120, 120, 155, 90, 195, 100, 210, 160, 180, 120, 300, 155, 210, 200, 280, 150, 360, 160, 315, 240, 270, 240, 455, 190, 300, 280, 450, 210, 480, 220, 420, 390, 360, 240, 620, 285, 465, 360, 490, 270, 600, 360, 600, 400, 450, 300, 840, 310, 480, 520, 635
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OFFSET
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1,1
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COMMENTS
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5 times the sum of the divisors of n.
a(n) is also the total number of horizontal rhombuses in the terraces of the n-th level of an irregular stepped pyramid (starting from the top) in which the structure of every 72-degree-three-dimensional sector arises after the 72-degree-zig-zag folding of every row of the diagram of the isosceles triangle A237593. The top of the pyramid is a five-pointed star formed by five rhombuses (see Links section).
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LINKS
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FORMULA
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MAPLE
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with(numtheory): seq(5*sigma(n), n=1..64);
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MATHEMATICA
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PROG
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(PARI) a(n) = 5 * sigma(n);
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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