A061599 -id:A061599 - cp's OEIS frontend

A061638 Primes p such that the greatest prime divisor of p-1 is 7.

29, 43, 71, 113, 127, 197, 211, 281, 337, 379, 421, 449, 491, 631, 673, 701, 757, 883, 1009, 1051, 1373, 1471, 2017, 2269, 2521, 2647, 2689, 2801, 3137, 3361, 3529, 4201, 4481, 5881, 6301, 7001, 7057, 7351, 7561, 7841, 8233, 8821, 10501, 10753, 12097

Offset: 1

Labos Elemer, Jun 13 2001

nonn

Prime numbers n for which cos(2*Pi/n) is an algebraic number of 7th degree. - Artur Jasinski, Dec 13 2006

			For n = {4, 8, 9, 12}, a(n)-1 = {70, 210, 280, 420} = 7*{10, 30, 40, 60}.

Harry J. Smith and Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (first 500 terms from Smith)

The 4th in a family of sequences after A019434(=Fermat-primes), A058383, A061599.
Cf. A019434, A058383, A023503, A034694, A006530, A006093, A035095, A061599.
Cf. A004729, A058383, A125867-A125875, A024899.

Select[Prime[Range[2000]],FactorInteger[#-1][[-1,1]] ==7&]  (* Harvey P. Dale, Mar 12 2011 *)

default(primelimit, 108864001); n=0; forprime (p=3, 108864001, f=factor(p - 1)~; if (f[1, length(f)]==7, write("b061638.txt", n++, " ", p))) \\ Harry J. Smith, Jul 25 2009

list(lim)=my(v=List(), t, t5, t7); lim\=1; lim--; for(a=1, logint(lim\2, 7), t7=2*7^a; for(b=0, logint(lim\t7, 5), t5=5^b*t7; for(c=0, logint(lim\t5, 3), t=3^c*t5; while(t<=lim, if(isprime(t+1), listput(v, t+1)); t<<=1)))); Set(v) \\ Charles R Greathouse IV, Oct 29 2018

Primes of form 2^a*3^b*5^c*7^d + 1 with a and d > 1.

A125868 Odd numbers k such that cos(2*Pi/k) is an algebraic number of a 5-smooth degree, but not 3-smooth.

Original entry on oeis.org

11, 25, 31, 33, 41, 55, 61, 75, 77, 93, 99, 101, 123, 125, 143, 151, 155, 165, 175, 181, 183, 187, 205, 209, 217, 225, 231, 241, 251, 271, 275, 279, 287, 297, 303, 305, 325, 341, 369, 375, 385, 401, 403, 407, 425, 427, 429, 451, 453, 465, 475, 495, 505, 525

Offset: 1

Artur Jasinski, Dec 13 2006

nonn

A regular polygon of a(n) sides can be constructed if one also has an angle trisector and 5-sector.

Cf. A058383, A061599, A125866-A125878.

Do[If[Take[FactorInteger[EulerPhi[2n+1]][[ -1]],1]=={5},Print[2n+1]],{n,1,1000}]

Edited by Don Reble, Apr 24 2007

cp's OEIS Frontend

A061638 Primes p such that the greatest prime divisor of p-1 is 7.

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