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A349717
a(n) is the smallest x such that sigma(x)/x = (3/2)*sigma(n)/n where sigma(n) is the sum of divisors of n or -1 if no such x exists.
1
2, 40, 6, 96, 10, 120, 14, 6528, 18, 1120, 22, 4320, 26, 280, 30, 16896, 34, 360, 38, 480, 42, 440, 46, 293760, 50, 520, 54, 120, 58, 3360, 62, 931840, 66, 680, 70, 2643840, 74, 760, 78, 32640, 82, 840, 86, 1056, 90, 920, 94, 760320, 98, 5600, 102, 1248, 106, 1080, 110
OFFSET
1,1
LINKS
EXAMPLE
For n=1, sigma(1) = 1, so a(1) = 2 since sigma(2)/2 = 3/2, so a(1) = 2.
PROG
(PARI) a(n) = my(q=3*sigma(n, -1)/2, k=1); while(sigma(k, -1) != q, k++); k;
(PARI) a(n) = {my(nv = 3*sigma(n)/(2*n), lim = 1, sv = []); while (#sv == 0, lim *= 10^10; sv = vecsort(solveBA(numerator(nv), denominator(nv), lim))); return (sv[1]); }
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Nov 26 2021
STATUS
approved