

A316476


Stable numbers. Numbers whose distinct prime indices are pairwise indivisible.


50



1, 2, 3, 4, 5, 7, 8, 9, 11, 13, 15, 16, 17, 19, 23, 25, 27, 29, 31, 32, 33, 35, 37, 41, 43, 45, 47, 49, 51, 53, 55, 59, 61, 64, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 89, 91, 93, 95, 97, 99, 101, 103, 107, 109, 113, 119, 121, 123, 125, 127, 128, 131, 135, 137
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OFFSET

1,2


COMMENTS

A prime index of n is a number m such that prime(m) divides n.


LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..10000


EXAMPLE

The prime indices of 45 are {2,2,3}, so the distinct prime indices are {2,3}, which are pairwise indivisible, so 45 belongs to the sequence.
The prime indices of 105 are {2,3,4}, which are not pairwise indivisible (2 divides 4), so 105 does not belong to the sequence.


MATHEMATICA

Select[Range[100], Select[Tuples[If[#===1, {}, Cases[FactorInteger[#], {p_, k_}:>PrimePi[p]]], 2], UnsameQ@@#&&Divisible@@#&]=={}&]


PROG

(PARI) ok(n)={my(v=apply(primepi, factor(n)[, 1])); for(j=2, #v, for(i=1, j1, if(v[j]%v[i]==0, return(0)))); 1} \\ Andrew Howroyd, Aug 26 2018


CROSSREFS

Cf. A056239, A112798, A285572, A285573, A303362, A304713, A316468, A316475.
Sequence in context: A115405 A257144 A328674 * A056867 A320324 A321698
Adjacent sequences: A316473 A316474 A316475 * A316477 A316478 A316479


KEYWORD

nonn


AUTHOR

Gus Wiseman, Jul 04 2018


STATUS

approved



