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 A318738 Numbers n=2*k-1 where Sum_{j=1..k} (-1)^(j+1) * d(2*j-1) achieves a new negative record, with d(n) = number of divisors of n (A000005). 5
 3, 15, 39, 63, 99, 259, 319, 403, 675, 679, 943, 1615, 1779, 2919, 4899, 5775, 7399, 7407, 13475, 13479, 25635, 29835, 29839, 44955, 78463, 78475, 108927, 108931, 126819, 136959, 136975, 136983, 244875, 244879, 256355, 276675, 276687, 457275, 530139 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Hugo Pfoertner, Table of n, a(n) for n = 1..282 EXAMPLE a(1) = 3, because s = d(1)-d(3) = 1-2 = -1 is the first negative record. a(2) = 15, because s = d(1)-d(3)+d(5)-d(7)+d(9)-d(11)+d(13)-d(15) = 1-2+2-2+3-2+2-4 = -2 is the first sum less than -1. PROG (PARI) s=0; j=-1; smin=0; forstep(k=1, 600000, 2, j=-j; s=s+j*numdiv(k); if(s

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Last modified March 29 09:20 EDT 2023. Contains 361598 sequences. (Running on oeis4.)