A320461 - OEIS

A320461

MM-numbers of labeled graphs with loops spanning an initial interval of positive integers.

1, 7, 13, 91, 161, 299, 329, 377, 611, 667, 1261, 1363, 1937, 2021, 2093, 2117, 2639, 4277, 4669, 7567, 8671, 8827, 9541, 13559, 14053, 14147, 14819, 15617, 16211, 17719, 23989, 24017, 26273, 27521, 28681, 29003, 31349, 31913, 36569, 44551, 44603, 46483, 48691

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

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. The multiset multisystem with MM-number n is formed by taking the multiset of prime indices of each part of the multiset of prime indices of n. For example, the prime indices of 78 are {1,2,6}, so the multiset multisystem with MM-number 78 is {{},{1},{1,2}}.

LINKS

Table of n, a(n) for n=1..43.

Eric Weisstein's World of Mathematics, Simple Graph

EXAMPLE

The sequence of terms together with their multiset multisystems begins:

1: {}

7: {{1,1}}

13: {{1,2}}

91: {{1,1},{1,2}}

161: {{1,1},{2,2}}

299: {{2,2},{1,2}}

329: {{1,1},{2,3}}

377: {{1,2},{1,3}}

611: {{1,2},{2,3}}

667: {{2,2},{1,3}}

1261: {{3,3},{1,2}}

1363: {{1,3},{2,3}}

1937: {{1,2},{3,4}}

2021: {{1,4},{2,3}}

2093: {{1,1},{2,2},{1,2}}

2117: {{1,3},{2,4}}

2639: {{1,1},{1,2},{1,3}}

4277: {{1,1},{1,2},{2,3}}

4669: {{1,1},{2,2},{1,3}}

MATHEMATICA

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

normQ[sys_]:=Or[Length[sys]==0, Union@@sys==Range[Max@@Max@@sys]];

Select[Range[10000], And[SquareFreeQ[#], normQ[primeMS/@primeMS[#]], And@@(Length[primeMS[#]]==2&/@primeMS[#])]&]

CROSSREFS

Cf. A003963, A005117, A055932, A056239, A112798, A255906, A290103, A302242, A305052.

Cf. A320456, A320458, A320459, A320462, A320532.

Sequence in context: A073220 A110455 A177952 * A132373 A110293 A253333

Adjacent sequences: A320458 A320459 A320460 * A320462 A320463 A320464

KEYWORD

nonn

AUTHOR

Gus Wiseman, Oct 13 2018

STATUS

approved