OFFSET
1,1
COMMENTS
Prime(i) such that A087273(i) <= 5.
LINKS
Robert Israel, Table of n, a(n) for n = 1..1645
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
KEYWORD
nonn
AUTHOR
Robert Israel, Sep 19 2016
STATUS
approved