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A340233
a(n) is the least number with exactly n exponential divisors.
5
1, 4, 16, 36, 65536, 144, 18446744073709551616, 576, 1296, 589824
OFFSET
1,2
COMMENTS
a(11) = 2^(2^10) has 309 digits and is too large to be included in the data section.
See the link for more values of this sequence.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..100 (given by prime factorizations)
FORMULA
A049419(a(n)) = n and A049419(k) != n for all k < a(n).
EXAMPLE
a(2) = 4 since 4 is the least number with 2 exponential divisors, 2 and 4.
MATHEMATICA
f[p_, e_] := DivisorSigma[0, e]; d[1] = 1; d[n_] := Times @@ (f @@@ FactorInteger[n]); max = 6; s = Table[0, {max}]; c = 0; n = 1; While[c < max, i = d[n]; If[i <= max && s[[i]] == 0, c++; s[[i]] = n]; n++]; s (* ineffective for n > 6 *)
CROSSREFS
Subsequence of A025487.
Similar sequences: A005179 (all divisors), A038547 (odd divisors), A085629 (coreful divisors), A309181 (nonunitary), A340232 (bi-unitary).
Sequence in context: A030158 A054246 A173545 * A080709 A256322 A080855
KEYWORD
nonn
AUTHOR
Amiram Eldar, Jan 01 2021
STATUS
approved