login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A316476 Stable numbers. Numbers whose distinct prime indices are pairwise indivisible. 14
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 (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.

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, j-1, 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: A088948 A115405 A257144 * A056867 A320324 A321698

Adjacent sequences:  A316473 A316474 A316475 * A316477 A316478 A316479

KEYWORD

nonn

AUTHOR

Gus Wiseman, Jul 04 2018

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 22 12:23 EDT 2019. Contains 321421 sequences. (Running on oeis4.)