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A081532
Triangle read by rows: let m be smallest number with n divisors, then row n gives divisors of m.
6
1, 1, 2, 1, 2, 4, 1, 2, 3, 6, 1, 2, 4, 8, 16, 1, 2, 3, 4, 6, 12, 1, 2, 4, 8, 16, 32, 64, 1, 2, 3, 4, 6, 8, 12, 24, 1, 2, 3, 4, 6, 9, 12, 18, 36, 1, 2, 3, 4, 6, 8, 12, 16, 24, 48, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096
OFFSET
1,3
LINKS
Eric Weisstein's World of Mathematics, Divisor
FORMULA
T(n,k) = k-th divisor of smallest number having exactly n divisors, 1<=k<=n.
T(n,1) = 1, T(n,n) = A005179(n); A000005(T(n,n)) = n.
EXAMPLE
Triangle begins
1;
1,2;
1,2,4;
1,2,3,6;
1,2,4,8,16;
1,2,3,4,6,12;
...
MATHEMATICA
Function[s, Map[Lookup[s, #] &, Range[First@ Complement[Range@ Max@ #, #] - 1]] &@ Keys@ s]@ Map[Divisors@ First@ # &, KeySort@ PositionIndex@ Array[DivisorSigma[0, #] &, 5000]] // Flatten (* Michael De Vlieger, Nov 15 2020 *)
CROSSREFS
Leading diagonal is A005179. Cf. A000005, A081533.
Sequence in context: A104778 A356184 A292477 * A174843 A253572 A141539
KEYWORD
nonn,tabl
AUTHOR
Amarnath Murthy, Mar 28 2003
EXTENSIONS
More terms from Sam Alexander, Oct 21 2003
More terms from Michel Marcus, Nov 15 2020
STATUS
approved