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A294013 Sum of the differences of the larger and smaller parts in the partitions of 2n into two parts with the smaller part prime. 2
0, 0, 2, 6, 10, 16, 22, 30, 38, 46, 54, 64, 74, 86, 98, 110, 122, 136, 150, 166, 182, 198, 214, 232, 250, 268, 286, 304, 322, 342, 362, 384, 406, 428, 450, 472, 494, 518, 542, 566, 590, 616, 642, 670, 698, 726, 754, 784, 814, 844, 874, 904, 934, 966, 998 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Sum of the slopes of the tangent lines along the left side of the parabola b(x) = 2*n*x-x^2 at prime values of x for x in 0 < x <= n. For example, d/dx 2*n*x-x^2 = 2n-2x. So for a(6), the prime values of x are x=2,3,5 and so a(6) = 12-2*2 + 12-2*3 + 12-2*5 = 8 + 6 + 2 = 16. - Wesley Ivan Hurt, Mar 24 2018
LINKS
FORMULA
a(n) = 2 * Sum_{i=1..n} (n - i) * A010051(i).
EXAMPLE
a(4) = 6: There are two partitions of 2*4 = 8 into two parts with the smaller part prime; they are (6,2) and (5,3). The sum of the differences of the parts is (6 - 2) + (5 - 3) = 4 + 2 = 6.
MATHEMATICA
Table[2 Sum[(n - i) (PrimePi[i] - PrimePi[i - 1]), {i, n}], {n, 40}]
Table[Total[#[[1]]-#[[2]]&/@Select[IntegerPartitions[2n, {2}], PrimeQ[ #[[2]]]&]], {n, 60}] (* Harvey P. Dale, Jan 25 2019 *)
CROSSREFS
Sequence in context: A220453 A195957 A354425 * A183575 A096184 A254829
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, Oct 21 2017
STATUS
approved

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Last modified April 22 12:13 EDT 2024. Contains 371900 sequences. (Running on oeis4.)