A347931 Nonprime numbers that divide their second arithmetic derivative.

1, 4, 8, 16, 24, 27, 48, 54, 64, 108, 128, 162, 168, 256, 320, 324, 432, 512, 704, 729, 864, 1024, 1134, 1728, 2048, 2160, 2187, 2192, 2916, 3125, 3456, 4096, 4752, 5120, 5832, 6250, 6912, 11664, 12500, 13824, 14580, 14796, 16384, 18750, 19683, 23328, 27648

Offset

1,2

Links

Alois P. Heinz, Table of n, a(n) for n = 1..250

Wikipedia, Arithmetic derivative

Formula

{ A348284 } minus { A000040 }.

{ A018252 } intersect { A348284 }.

Maple

d:= n-> n*add(i[2]/i[1], i=ifactors(n)[2]):
q:= n-> not isprime(n) and irem(d(d(n)), n)=0:
select(q, [$1..30000])[];  # Alois P. Heinz, Oct 15 2021

Crossrefs

Cf. A000040, A003415, A018252, A068346, A348284.

Sequence in context: A312823 A133690 A097057 * A354810 A333168 A306219

Adjacent sequences: A347928 A347929 A347930 * A347932 A347933 A347934

Keyword

nonn

Author

Alois P. Heinz, Oct 15 2021

Status

approved