A306202 - OEIS

A306202

Matula-Goebel numbers of rooted semi-identity trees.

1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 19, 20, 21, 22, 24, 26, 28, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 40, 41, 42, 43, 44, 47, 48, 51, 52, 53, 55, 56, 57, 58, 59, 60, 62, 64, 65, 66, 67, 68, 70, 71, 73, 74, 76, 77, 78, 79, 80, 82, 84, 85

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OFFSET

1,2

COMMENTS

Definition: A positive integer belongs to the sequence iff its prime indices greater than 1 are distinct and already belong to the sequence. A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

LINKS

Table of n, a(n) for n=1..67.

Index entries for sequences related to Matula-Goebel numbers

EXAMPLE

The sequence of all unlabeled rooted semi-identity trees together with their Matula-Goebel numbers begins:

1: o

2: (o)

3: ((o))

4: (oo)

5: (((o)))

6: (o(o))

7: ((oo))

8: (ooo)

10: (o((o)))

11: ((((o))))

12: (oo(o))

13: ((o(o)))

14: (o(oo))

15: ((o)((o)))

16: (oooo)

17: (((oo)))

19: ((ooo))

20: (oo((o)))

21: ((o)(oo))

22: (o(((o))))

24: (ooo(o))

26: (o(o(o)))

28: (oo(oo))

29: ((o((o))))

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

MATHEMATICA

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

psidQ[n_]:=And[UnsameQ@@DeleteCases[primeMS[n], 1], And@@psidQ/@primeMS[n]];

Select[Range[100], psidQ]

CROSSREFS

Cf. A000081, A004111, A007097, A276625, A277098, A306200, A306201, A316467.

Sequence in context: A347243 A325389 A020662 * A328335 A302569 A235034

Adjacent sequences: A306199 A306200 A306201 * A306203 A306204 A306205

KEYWORD

nonn

AUTHOR

Gus Wiseman, Jan 29 2019

STATUS

approved