A276827 Primes p such that the greatest prime factor of 3*p+1 is at most 5.

3, 5, 13, 53, 83, 853, 2083, 3413, 5333, 85333, 208333, 218453, 341333, 3495253, 5461333, 8533333, 13981013, 83333333, 853333333, 22369621333, 218453333333, 341333333333, 2236962133333, 3665038759253, 53333333333333, 91625968981333, 203450520833333, 1333333333333333

Offset: 1

Author

Robert Israel, Sep 19 2016

Keywords

• nonn

Comments

Prime(i) such that A087273(i) <= 5.

Links

• Robert Israel, Table of n, a(n) for n = 1..1645

Crossrefs

Cf. A087273.

Contains A093671, A093674, and A093676.

Programs

Maple

N = 10^20: # to get all terms <= N
Res:= {}:
for a from 0 to ilog2(floor((3*N+1)/5)) do
  twoa:= 2^a;
  for b from (a mod 2) by 2 do
    p:= (twoa*5^b-1)/3;
    if p > N then break fi;
    if isprime(p) then
      Res:= Res union {p};
    fi
od od:
sort(convert(Res,list));

Mathematica

Select[Prime@ Range[10^6], FactorInteger[3 # + 1][[-1, 1]] <= 5 &] (* Michael De Vlieger, Sep 19 2016 *)

PARI

list(lim)=my(v=List(),s,t); lim=lim\1*3 + 1; for(i=0,logint(lim\2,5), t=if(i%2,2,4)*5^i; while(t<=lim, if(isprime(p=t\3), listput(v,p)); t<<=2)); Set(v) \\ Charles R Greathouse IV, Sep 19 2016