OFFSET
1,1
COMMENTS
Prime numbers n for which cos(2Pi/n) is an algebraic number of 5th degree. - Artur Jasinski, Dec 13 2006
The least significant digit of each term is one. - Harvey P. Dale, Jul 07 2024
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
FORMULA
Primes of the form 2^a*3^b*5^c + 1 with a and c > 0.
MATHEMATICA
Do[If[Take[FactorInteger[EulerPhi[2n + 1]][[ -1]], 1] == {5} && PrimeQ[2n + 1], Print[2n + 1]], {n, 1, 10000}] (* Artur Jasinski, Dec 13 2006 *)
Select[Prime[Range[3000]], Max[FactorInteger[#-1][[;; , 1]]]==5&] (* Harvey P. Dale, Jul 07 2024 *)
PROG
(PARI) { default(primelimit, 167772161); n=0; forprime (p=3, 167772161, f=factor(p - 1)~; if (f[1, length(f)]==5, write("b061599.txt", n++, " ", p)) ) } \\ Harry J. Smith, Jul 25 2009
(PARI) list(lim)=my(v=List(), s, t); lim\=1; lim--; for(i=1, logint(lim\2, 5), t=2*5^i; for(j=0, logint(lim\t, 3), s=t*3^j; while(s<=lim, if(isprime(s+1), listput(v, s+1)); s<<=1))); Set(v) \\ Charles R Greathouse IV, Oct 29 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jun 13 2001
STATUS
approved