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A276827
Primes p such that the greatest prime factor of 3*p+1 is at most 5.
1
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
1,1
COMMENTS
Prime(i) such that A087273(i) <= 5.
LINKS
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 *)
PROG
(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
CROSSREFS
Cf. A087273.
Contains A093671, A093674, and A093676.
Sequence in context: A106879 A249762 A264812 * A034375 A081953 A181848
KEYWORD
nonn
AUTHOR
Robert Israel, Sep 19 2016
STATUS
approved