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!)
A340799 a(n) is the smallest prime p such that p + 1 has 2n divisors. 3
2, 5, 11, 23, 47, 59, 191, 167, 179, 239, 5119, 359, 20479, 2111, 719, 839, 1114111, 1259, 786431, 3023, 2879, 15359, 348127231, 3359, 22031, 266239, 6299, 6719, 22280142847, 5039, 559419490303, 7559, 156671, 7798783, 25919, 10079, 1168231104511, 5505023 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
A000005(a(n) + 1) = 2n.
EXAMPLE
a(4) = 23 because 23 is the smallest prime p such that p + 1 has 2*4 divisors; tau(24) = 8.
PROG
(Magma) Ax:=func<n|exists(r){m:m in[1..10^7] | IsPrime(m) and #Divisors(m + 1) eq n*#Divisors(m)}select r else 0>; [Ax(n): n in[1..20]]
CROSSREFS
Cf. A000005 (tau), A003680, A080371.
Sequence in context: A349411 A347309 A174162 * A186253 A226462 A000100
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Jan 21 2021
STATUS
approved

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 14:02 EDT 2024. Contains 371254 sequences. (Running on oeis4.)