A347931 - OEIS

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A347931

Nonprime numbers that divide their second arithmetic derivative.

1

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

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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