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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 (list; graph; refs; listen; history; text; internal format)
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

Cf. A087273.

Contains A093671, A093674, and A093676.

Sequence in context: A106879 A249762 A264812 * A034375 A081953 A181848

Adjacent sequences:  A276824 A276825 A276826 * A276828 A276829 A276830

KEYWORD

nonn

AUTHOR

Robert Israel, Sep 19 2016

STATUS

approved

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Last modified December 1 20:01 EST 2021. Contains 349430 sequences. (Running on oeis4.)