A290822 - OEIS

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A290822

Transitive numbers: Matula-Goebel numbers of transitive rooted trees.

1, 2, 4, 6, 8, 12, 14, 16, 18, 24, 28, 30, 32, 36, 38, 42, 48, 54, 56, 60, 64, 72, 76, 78, 84, 90, 96, 98, 106, 108, 112, 114, 120, 126, 128, 138, 144, 150, 152, 156, 162, 168, 180, 192, 196, 210, 212, 216, 222, 224, 228, 234, 238, 240, 252, 256, 262, 266, 270

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OFFSET

1,2

COMMENTS

A number x is transitive if whenever prime(y) divides x and prime(z) divides y, we have prime(z) divides x.

LINKS

Robert P. P. McKone, Table of n, a(n) for n = 1..9999

EXAMPLE

The sequence of transitive rooted trees begins:

1 o

2 (o)

4 (oo)

6 (o(o))

8 (ooo)

12 (oo(o))

14 (o(oo))

16 (oooo)

18 (o(o)(o))

24 (ooo(o))

28 (oo(oo))

30 (o(o)((o)))

32 (ooooo)

36 (oo(o)(o))

38 (o(ooo))

42 (o(o)(oo))

48 (oooo(o))

54 (o(o)(o)(o))

56 (ooo(oo))

60 (oo(o)((o)))

64 (oooooo)

72 (ooo(o)(o))

76 (oo(ooo))

78 (o(o)(o(o)))

84 (oo(o)(oo))

90 (o(o)(o)((o)))

96 (ooooo(o))

98 (o(oo)(oo))

MATHEMATICA

primeMS[n_]:=If[n===1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];

subprimes[n_]:=If[n===1, {}, Union@@Cases[FactorInteger[n], {p_, _}:>FactorInteger[PrimePi[p]][[All, 1]]]];

Select[Range[270], Divisible[#, Times@@subprimes[#]]&]

CROSSREFS

Cf. A007097, A276625, A279861, A290689, A290760.

Sequence in context: A217562 A088879 A316470 * A318186 A139363 A091065

Adjacent sequences: A290819 A290820 A290821 * A290823 A290824 A290825

KEYWORD

nonn

AUTHOR

Gus Wiseman, Oct 19 2017

STATUS

approved