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A273103
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Sum of the elements of the difference triangle of the divisors of n (including the divisors of n).
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14
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1, 4, 6, 11, 10, 21, 14, 26, 25, 31, 22, 52, 26, 41, 54, 57, 34, 86, 38, 66, 72, 61, 46, 103, 71, 71, 90, 102, 58, 205, 62, 120, 108, 91, 134, 157, 74, 101, 126, 75, 82, 329, 86, 174, 218, 121, 94, 110, 141, 158, 162, 210, 106, 373, 202, 269, 180, 151, 118, -437, 122, 161, 250
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OFFSET
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1,2
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COMMENTS
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a(n) is the sum of the n-th slice of the tetrahedron A273102.
First differs from A187215 at a(14).
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LINKS
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FORMULA
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a(n) = 2n, if n is prime.
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EXAMPLE
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For n = 14 the divisors of 14 are 1, 2, 7, 14, and the difference triangle of the divisors is
1 . 2 . 7 . 14
. 1 . 5 . 7
. . 4 . 2
. . .-2
The sum of all elements of the triangle is 1 + 2 + 7 + 14 + 1 + 5 + 7 + 4 + 2 - 2 = 41, so a(14) = 41.
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MATHEMATICA
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Table[Total@ Flatten@ NestWhileList[Differences, Divisors@ n, Length@ # > 1 &], {n, 63}] (* Michael De Vlieger, May 17 2016 *)
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PROG
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(PARI) a(n) = {my(d = divisors(n)); my(s = vecsum(d)); for (k=1, #d-1, d = vector(#d-1, n, d[n+1] - d[n]); s += vecsum(d); ); s; } \\ Michel Marcus, May 16 2016
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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