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A358514
a(n) is the smallest number with exactly n divisors that are Achilles numbers (A052486).
0
1, 72, 216, 432, 1296, 864, 7200, 2592, 6912, 10800, 7776, 15552, 27000, 41472, 21600, 31104, 884736, 54000, 64800, 129600, 86400, 248832, 172800, 162000, 5308416, 108000, 194400, 216000, 518400, 388800, 810000, 1323000, 1058400, 1382400, 324000, 432000, 2073600
OFFSET
0,2
EXAMPLE
1 has no Achilles number divisors, so a(0) = 1.
72 = A052486(1), so a(1) = 72.
216 has divisors 72 = A052486(1) and 108 = A052486(2), and there are no smaller numbers that have exactly two divisors that are Achilles numbers, so a(2) = 216.
PROG
(Magma) ah:=func<n|n ne 1 and forall{i:i in [1..#Factorisation(n)] |Factorisation(n)[i][2] gt 1} and Gcd([Factorisation(n)[i][2] :i in [1..#Factorisation(n)]]) eq 1>; a:=[]; for n in [0..37] do k:=1; while #[d:d in Divisors(k)| ah(d)] ne n do k:=k+1; end while; Append(~a, k); end for; a;
(PARI) is(n) = my(f=factor(n)[, 2]); n>9 && vecmin(f)>1 && gcd(f)==1; \\ A052486
a(n) = my(k=1); while (sumdiv(k, d, is(d)) != n, k++); k; \\ Michel Marcus, Dec 13 2022
CROSSREFS
Sequence in context: A235179 A204492 A204485 * A344179 A050498 A077535
KEYWORD
nonn
AUTHOR
Marius A. Burtea, Dec 04 2022
STATUS
approved