A242824
Primes formed by the initial digits of the decimal expansion of 1/7, starting at the first nonzero digit in the expansion.
Original entry on oeis.org
1428571, 1428571428571428571428571
Offset: 1
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Select[Table[FromDigits[PadRight[{},6n+1,{1,4,2,8,5,7}]],{n,200}],PrimeQ](* Harvey P. Dale, Oct 03 2018 *)
A242833
Primes formed by the initial digits of the decimal expansion of 1/19, starting at the first nonzero digit in the expansion.
Original entry on oeis.org
5, 52631, 5263157894736842105263157, 52631578947368421052631578947368421052631578947368421052631
Offset: 1
-
lista(nn) = {v = [5,2,6,3,1,5,7,8,9,4,7,3,6,8,4,2,1,0]; n = 0; for (i=0, nn, n = 10*n+ v[(i % 18)+1]; if (ispseudoprime(n), print1(n, ", ")););} \\ Michel Marcus, May 27 2014
A242826
Primes formed by the initial digits of the decimal expansion of 1/13, starting at the first nonzero digit in the expansion.
Original entry on oeis.org
7, 769, 769230769, 769230769230769230769, 769230769230769230769230769230769
Offset: 1
A242827
Primes formed by the initial digits of the decimal expansion of 1/14, starting at the first nonzero digit in the expansion.
Original entry on oeis.org
7, 71, 71428571, 7142857142857, 7142857142857142857142857142857
Offset: 1
-
lista(nn) = {v = [7,1,4,2,8,5]; n = 0; for (i=0, nn, n = 10*n+ v[(i % 6)+1]; if (ispseudoprime(n), print1(n, ", ")););} \\ Michel Marcus, May 26 2014
A242828
Primes formed by the initial digits of the decimal expansion of 1/17, starting at the first nonzero digit in the expansion.
Original entry on oeis.org
5, 5882352941, 588235294117, 588235294117647058823529411764705882352941176470588235294117
Offset: 1
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Select[Table[FromDigits[PadRight[{},n,{5,8,8,2,3,5,2,9,4,1,1,7,6,4,7,0}]],{n,60}],PrimeQ] (* Harvey P. Dale, Aug 08 2021 *)
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lista(nn) = {v = [5, 8, 8, 2, 3, 5, 2, 9, 4, 1, 1, 7, 6, 4, 7, 0]; n = 0; for (i=0, nn, n = 10*n+ v[(i % 16)+1]; if (ispseudoprime(n), print1(#Str(n), ", ")););} \\ Michel Marcus, May 27 2014
A056723
Numbers k such that 8*10^k + 3*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Original entry on oeis.org
1, 7, 23, 29, 133, 173, 367, 1925, 3707, 5765, 9709, 19573, 43753
Offset: 1
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Do[ If[ PrimeQ[ 8*10^n + 3*(10^n-1)/9], Print[n]], {n, 0, 10000}]
Corrected by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
19573 and 43753 from Serge Batalov, Jan 2009 confirmed as next terms by
Ray Chandler, Feb 13 2012
A276827
Primes p such that the greatest prime factor of 3*p+1 is at most 5.
Original entry on oeis.org
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
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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));
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Select[Prime@ Range[10^6], FactorInteger[3 # + 1][[-1, 1]] <= 5 &] (* Michael De Vlieger, Sep 19 2016 *)
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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
Showing 1-7 of 7 results.
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