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!)
A072344 a(n) = the least natural number k such that k*phi(n) + 1 is prime. 3
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 1, 1, 2, 1, 1, 2, 1, 3, 1, 1, 1, 3, 1, 1, 1, 1, 2, 3, 1, 1, 1, 1, 2, 3, 3, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 2, 2, 1, 3, 2, 3, 1, 3, 1, 1, 1, 1, 1, 3, 1, 3, 2, 1, 1, 3, 3, 1, 2, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,15

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A034693(A000010(n)). - Antti Karttunen, Aug 22 2017

EXAMPLE

phi(35) = 24 and the least natural number k such that 24 k + 1 is prime is k = 3; so a(35) = 3.

MATHEMATICA

f[n_] := Module[{i}, i = 0; While[ ! PrimeQ[i*EulerPhi[n] + 1], i++ ]; i]; Table[f[i], {i, 1, 150}]

PROG

(PARI)

A034693(n) = { my(k=1); while(!isprime(1+(k*n)), k++); k; };

A072344(n) = A034693(eulerphi(n)); \\ Antti Karttunen, Aug 22 2017

CROSSREFS

Cf. A000010, A034693, A072917.

Sequence in context: A243840 A117898 A212810 * A140500 A156054 A030616

Adjacent sequences:  A072341 A072342 A072343 * A072345 A072346 A072347

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Jul 16 2002

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 August 17 12:30 EDT 2022. Contains 356189 sequences. (Running on oeis4.)