login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A341099 Numbers divisible by at least three terms of A008864. 2

%I #21 May 16 2023 10:39:42

%S 12,18,24,30,32,36,40,42,48,54,56,60,64,72,80,84,88,90,96,102,104,108,

%T 112,114,120,126,128,132,136,138,140,144,150,152,156,160,162,168,174,

%U 176,180,186,192,196,198,200,204,208,210,216,220,222,224,228,234,240,248,252,256,258,264,270,272

%N Numbers divisible by at least three terms of A008864.

%C Numbers divisible by p+1 for at least three primes p.

%C Numbers k with A072627(k) >= 3.

%C Every positive multiple of a term is a term.

%H Robert Israel, <a href="/A341099/b341099.txt">Table of n, a(n) for n = 1..10000</a>

%e a(4) = 30 is a term because it is divisible by 2+1=3, 5+1=6 and 29+1=30.

%p filter:= proc(n) local D;

%p D:= convert(numtheory:-divisors(n),list);

%p numboccur(true, map(t -> isprime(t-1),D))>= 3

%p end proc:

%p select(filter, [$1..1000]);

%t okQ[n_] := DivisorSum[n, Boole[PrimeQ[#-1]]&] >= 3;

%t Select[Range[1000], okQ] (* _Jean-François Alcover_, May 16 2023 *)

%o (PARI) isok(m) = sumdiv(m, d, isprime(d-1)) >= 3; \\ _Michel Marcus_, Feb 05 2021

%Y Cf. A005101, A005835, A008864, A072627.

%K nonn

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Feb 04 2021

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 13:35 EDT 2024. Contains 371254 sequences. (Running on oeis4.)