A328189 - OEIS

A328189

Numbers n with at least one pair of consecutive divisible nontrivial divisors (greater than 1 and less than n).

8, 16, 18, 20, 27, 28, 32, 40, 42, 44, 50, 52, 54, 56, 64, 66, 68, 75, 76, 78, 80, 81, 88, 92, 98, 99, 100, 102, 104, 110, 112, 114, 116, 117, 124, 125, 126, 128, 130, 136, 138, 140, 147, 148, 152, 153, 156, 160, 162, 164, 170, 171, 172, 174, 176, 184, 186

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..57.

EXAMPLE

The nontrivial divisors of 42 are {2, 3, 6, 7, 14, 21}, with pairs of consecutive divisible divisors {3, 6} and {7, 14}, so 42 belongs to the sequence.

MATHEMATICA

Select[Range[200], MatchQ[DeleteCases[Divisors[#], 1|#], {___, x_, y_, ___}/; Divisible[y, x]]&]

Select[Range[2, 200], AnyTrue[Partition[Most[Rest[Divisors[#]]], 2, 1], Mod[#[[2]], #[[1]]] == 0&]&] (* Harvey P. Dale, Mar 14 2023 *)

CROSSREFS

Complement of A328161.

Positions of terms greater than 1 in A328194.

Partitions with a pair of consecutive divisible parts are A328221.

Cf. A000005, A060680, A060775, A067513, A088725, A163870, A328028, A328162, A328171.

Sequence in context: A247061 A180860 A356450 * A101766 A338930 A357002

Adjacent sequences: A328186 A328187 A328188 * A328190 A328191 A328192

KEYWORD

nonn

AUTHOR

Gus Wiseman, Oct 13 2019

STATUS

approved