login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A134765 Least prime p for which (p-1)/2 - phi(p-1) = n, or 0 if there is no such prime. 2
3, 7, 13, 19, 41, 0, 37, 31, 113, 43, 101, 71, 73, 67, 61, 79, 97, 131, 109, 103, 0, 0, 0, 191, 0, 139, 677, 127, 0, 419, 157, 0, 193, 0, 0, 151, 0, 0, 0, 199, 401, 683, 181, 0, 281, 0, 0, 431, 0, 283, 277, 0, 0, 659, 461, 0, 241, 211, 0, 743, 313, 0, 349, 271, 641, 827 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

The graph of this sequence shows that for n>8 either a(n)=0 or a(n)<=1+n^2. See A098006 for the values of (p-1)/2 - phi(p-1) for odd primes p. Sequence A098047 lists the n for which a(n)=0. A134854(n)=a(2^(n-1)).

LINKS

T. D. Noe, Table of n, a(n) for n = 0..10000

T. D. Noe, Finding primes p for which (p-1)/2 - phi(p-1) = k

T. D. Noe, Graph for n <= 50000

MATHEMATICA

nn=1000; lc=Table[0, {nn}]; Do[p=Prime[n]; r=(p-1)/2-EulerPhi[p-1]; If[0<r<=nn && lc[[r]]==0, lc[[r]]=p], {n, 2, PrimePi[1+nn^2]}]; PrependTo[lc, 3]

CROSSREFS

Sequence in context: A098044 A252091 A217035 * A023230 A194581 A106080

Adjacent sequences:  A134762 A134763 A134764 * A134766 A134767 A134768

KEYWORD

nonn

AUTHOR

T. D. Noe, Nov 13 2007, Nov 19 2007

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 August 4 21:32 EDT 2021. Contains 346455 sequences. (Running on oeis4.)