A020449 -id:A020449 - cp's OEIS frontend

A100580 Palindromic primes containing digits 0 and 1 only. (Palindromic terms in A020449.)

11, 101, 100111001, 110111011, 111010111, 1100011100011, 1100101010011, 1101010101011, 1110110110111, 1110111110111, 100110101011001, 101000010000101, 101011000110101, 101110000011101, 110011101110011

Offset: 1

Chuck Seggelin (seqfan(AT)plastereddragon.com), Nov 29 2004

			a(3) = 100111001 because 100111001 is the third palindromic prime composed only of 1's and 0's.

Jon E. Schoenfield, Table of n, a(n) for n = 1..15185 (all terms < 10^38; terms 1..200 from T. D. Noe, 201..2385 from Chai Wah Wu)

Cf. A020449, A002385, A000040, A002113.

PalQ[n_]:=FromDigits[Reverse@IntegerDigits[n]]==n; DeleteDuplicates[Flatten[Table[Select[FromDigits /@ Tuples[{0,1},n],PrimeQ[#]&&PalQ[#] &],{n,15}]]] (* Jayanta Basu, May 11 2013 *)
Select[FromDigits/@Tuples[{0,1},15],PalindromeQ[#]&&PrimeQ[#]&] (* Harvey P. Dale, Jan 18 2023 *)

from sympy import isprime
A100580_list = [11]
for i in range(2, 2**16):
    s = format(i, 'b')
    x = int(s+s[-2::-1])
    if isprime(x):
        A100580_list.append(x) # Chai Wah Wu, Jan 06 2015

A004022 Primes of the form (10^k - 1)/9. Also called repunit primes or repdigit primes.

Original entry on oeis.org

11, 1111111111111111111, 11111111111111111111111

Offset: 1

N. J. A. Sloane

The next term corresponds to k = 317 and is too large to include: see A004023.
Also called repunit primes or prime repunits.
Also, primes with digital product = 1.
The number of 1's in these repunits must also be prime. Since the number of 1's in (10^k-1)/9 is k, if k = p*m then (10^(p*m)-1) = (10^p)^m-1 => (10^p-1)/9 = q and q divides (10^k-1). This follows from the identity a^k - b^k = (a-b)*(a^(k-1) + a^(k-2)*b + ... + b^(k-1)). - Cino Hilliard, Dec 23 2008
A subset of A020449, ..., A020457, A036953, ..., cf. link to OEIS index. - M. F. Hasler, Jul 27 2015
The terms in this sequence, except 11 which is not Brazilian, are prime repunits in base ten, so they are Brazilian primes belonging to A085104 and A285017. - Bernard Schott, Apr 08 2017

T. M. Apostol, Introduction to Analytic Number Theory, Springer-Verlag, 1976, p. 11. Graham, Knuth and Patashnik, Concrete mathematics, Addison-Wesley, 1994; see p. 146, problem 22.
M. Barsanti, R. Dvornicich, M. Forti, T. Franzoni, M. Gobbino, S. Mortola, L. Pernazza and R. Romito, Il Fibonacci N. 8 (included in Il Fibonacci, Unione Matematica Italiana, 2011), 2004, Problem 8.10.
Clifford A. Pickover, A Passion for Mathematics, Wiley, 2005; see p. 60.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
James J. Tattersall, Elementary Number Theory in Nine Chapters, Cambridge University Press, 1999, page 114.

T. D. Noe, Table of n, a(n) for n = 1..5
J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
Ernest G. Hibbs, Component Interactions of the Prime Numbers, Ph. D. Thesis, Capitol Technology Univ. (2022), see p. 33.
Dmytro S. Inosov and Emil Vlasák, Cryptarithmically unique terms in integer sequences, arXiv:2410.21427 [math.NT], 2024. See p. 18.
Makoto Kamada, Factorizations of 11...11 (Repunit).
D. H. Lehmer, On the number (10^23-1)/9, Bull. Amer. Math. Soc. 35 (1929), 349-350.
James Maynard and Brady Haran, Primes without a 7, Numberphile video (2019)
Andy Steward, Prime Generalized Repunits
S. S. Wagstaff, Jr., The Cunningham Project
Index to entries for primes with digits in a given set.

Subsequence of A020449.
A116692 is another version of repunit primes or repdigit primes. - N. J. A. Sloane, Jan 22 2023
See A004023 for the number of 1's.
Cf. A046413.

[a: n in [0..300] | IsPrime(a) where a is (10^n - 1) div 9 ]; // Vincenzo Librandi, Nov 08 2014

lst={}; Do[If[PrimeQ[p = (10^n - 1)/9], AppendTo[lst, p]], {n, 10^2}]; lst (* Vladimir Joseph Stephan Orlovsky, Aug 22 2008 *)
Select[Table[(10^n - 1) / 9, {n, 500}], PrimeQ] (* Vincenzo Librandi, Nov 08 2014 *)
Select[Table[FromDigits[PadRight[{},n,1]],{n,30}],PrimeQ] (* Harvey P. Dale, Apr 07 2018 *)

forprime(x=2,20000,if(ispseudoprime((10^x-1)/9),print1((10^x-1)/9","))) \\ Cino Hilliard, Dec 23 2008

from sympy import isprime
from itertools import count, islice
def agen(): # generator of terms
    yield from (t for t in (int("1"*k) for k in count(1)) if isprime(t))
print(list(islice(agen(), 4))) # Michael S. Branicky, Jun 09 2022

a(n) = A002275(A004023(n)).

Edited by Max Alekseyev, Nov 15 2010

Name expanded by N. J. A. Sloane, Jan 22 2023

A089971 Primes whose decimal representation also represents a prime in base 2.

Original entry on oeis.org

11, 101, 10111, 101111, 1011001, 1100101, 10010101, 10011101, 10100011, 10101101, 10110011, 11000111, 11100101, 100111001, 101001011, 101101111, 101111011, 101111111, 110111011, 111001001, 1000001011, 1001001011, 1001110111, 1010000011, 1010000111, 1010001101

Offset: 1

Cino Hilliard, Jan 18 2004

See A065720 for the primes given by these terms considered as numbers written in base 2, i.e., the sequence with the definition "working in the opposite sense". - M. F. Hasler, Jan 05 2014

A subsequence of A020449. - M. F. Hasler, Jan 11 2014

			a(1)=11 is a prime and its decimal representation is also a valid base-2 representation (because all digits are < 2), and 11_2 = 3_10 is again a prime.

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Alejandro J. Becerra Jr., Python code for computing terms of A089971, A089981, A090707-A090710, A235394-A235395.
Alejandro J. Becerra Jr., Table of n, a(n) for n = 1..42012

Cf. A031974, A089981, A090707, A090708, A090709, A090710, A235394, A235395, A000040 and references therein.

Select[ FromDigits@# & /@ IntegerDigits[ Prime@ Range@ 270, 2], PrimeQ] (* Robert G. Wilson v, Jan 05 2014 *)

is_A089971(p)=vecmax(d=digits(p))<2&&isprime(vector(#d, i, 2^(#d-i))*d~)&&isprime(p) \\ "d" is implicitly declared local. Putting isprime(p) to the end improves performance when the function is applied to primes only or to very large numbers. - M. F. Hasler, Jan 05 2014

fixBase(n, oldBase, newBase)=my(d=digits(n, oldBase), t=newBase-1); for(i=1, #d, if(d[i]>t, for(j=i, #d, d[j]=t); break)); fromdigits(d, newBase)
list(lim)=my(v=List(), t); forprime(p=2, fixBase(lim\1, 10, 2), if(isprime(t=fromdigits(digits(p, 2), 10)), listput(v, t))); Vec(v) \\ Charles R Greathouse IV, Nov 07 2016

from sympy import isprime, primerange
def aupto(limit):
    alst = []
    for p in primerange(2, limit+1):
        t = int(bin(p)[2:])
        if isprime(t): alst.append(t)
    return alst
print(aupto(2**11)) # Michael S. Branicky, Aug 19 2021

Definition and example reworded, offset corrected, and cross-references added by M. F. Hasler, Jan 05 2014

A235265 Primes whose base-3 representation also is the base-2 representation of a prime.

Original entry on oeis.org

3, 13, 31, 37, 271, 283, 733, 757, 769, 1009, 1093, 2281, 2467, 2521, 2551, 2917, 3001, 3037, 3163, 3169, 3187, 3271, 6673, 7321, 7573, 9001, 9103, 9733, 19801, 19963, 20011, 20443, 20521, 20533, 20749, 21871, 21961, 22123, 22639, 22717, 27253, 28711, 28759, 29173, 29191, 59077, 61483, 61507, 61561, 65701, 65881

Offset: 1

M. F. Hasler, Jan 05 2014

This sequence and A235383 and A229037 are winners in the contest held at the 2014 AMS/MAA Joint Mathematics Meetings. - T. D. Noe, Jan 20 2014
This sequence was motivated by work initiated by V.J. Pohjola's post to the SeqFan list, which led to a clarification of the definition and correction of some errors, in sequences A089971, A089981 and A090707 through A090721. These sequences use "rebasing" (terminology of A065361) from some base b to base 10. Sequences A065720 - A065727 follow the same idea but use rebasing in the other sense, from base 10 to base b. The observation that only (10,b) and (b,10) had been considered so far led to the definition of this and related sequences: In a systematic approach, it seems natural to start with the smallest possible pairs of different bases, (2,3) and (3,2), then (2 <-> 4), (3 <-> 4), (2 <-> 5), etc.
Among the two possibilities using the smallest possible bases, 2 and 3, the present one seems a little bit more interesting, among others because not every base-3 representation is a valid base-2 representation (in contrast to the opposite case). This is also a reason why the present sequence grows much faster than the partner sequence A235266.

			3 = 10_3 and 10_2 = 2 is prime. 13 = 111_3 and 111_2 = 7 is prime.

Robert Israel, Table of n, a(n) for n = 1..10000
M. F. Hasler, Primes whose base c expansion is also the base b expansion of a prime
Veikko Pohjola, A090709 Decimal primes whose decimal representation in base 6 is also prime, SeqFan list, Jan 03 2014.

Subset of A077717.

Cf. A235266, A065720 and A036952, A065721 - A065727, A235394, A235395, A089971 and A020449, A089981, A090707 - A091924, A235461 - A235482. See M. F. Hasler's OEIS wiki page for further cross-references.

N:= 1000: # to get the first N terms
count:= 0:
for i from 1 while count < N do
   p2:= ithprime(i);
   L:= convert(p2,base,2);
   p3:= add(3^(j-1)*L[j],j=1..nops(L));
   if isprime(p3) then
      count:= count+1;
      A235265[count]:= p3;
   fi
od:
[seq(A235265[i], i=1..N)]; # Robert Israel, May 04 2014

b32pQ[n_]:=Module[{idn3=IntegerDigits[n,3]},Max[idn3]<2&&PrimeQ[ FromDigits[ idn3,2]]]; Select[Prime[Range[7000]],b32pQ] (* Harvey P. Dale, Apr 24 2015 *)

is(p,b=2,c=3)=vecmax(d=digits(p,c))

from sympy import isprime, nextprime
def agen(): # generator of terms
    p = 2
    while True:
        p3 = sum(3**i for i, bi in enumerate(bin(p)[2:][::-1]) if bi=='1')
        if isprime(p3):
            yield p3
        p = nextprime(p)
g = agen()
print([next(g) for n in range(1, 52)]) # Michael S. Branicky, Jan 16 2022

A235482 Primes whose base-5 representation is also the base-9 representation of a prime.

Original entry on oeis.org

2, 3, 7, 11, 17, 19, 37, 41, 61, 67, 71, 97, 109, 131, 139, 149, 151, 157, 167, 191, 197, 211, 251, 269, 281, 337, 349, 367, 401, 409, 439, 449, 457, 467, 487, 491, 499, 521, 557, 569, 607, 619, 631, 647, 661, 739, 761, 769, 821, 829, 887, 907, 941, 947, 967, 1009, 1019, 1031, 1061, 1069, 1087

Offset: 1

M. F. Hasler, Jan 12 2014

This sequence is part of a two-dimensional array of sequences, given in the LINK, based on this same idea for any two different bases b, c > 1. Sequence A235265 and A235266 are the most elementary ones in this list. Sequences A089971, A089981 and A090707 through A090721, and sequences A065720 - A065727, follow the same idea with one base equal to 10.

A subsequence of A197636 and of course of A000040 ⊂ A015919.

			41 = 131_5 and 131_9 = 109 are both prime, so 41 is a term.

Giovanni Resta, Table of n, a(n) for n = 1..10000
M. F. Hasler, Primes whose base c expansion is also the base b expansion of a prime

Cf. A235265, A235266, A235461 - A235481, A065720 ⊂ A036952, A065721 - A065727, A089971 ⊂ A020449, A089981, A090707 - A091924, A235394, A235395. See the LINK for further cross-references.

Select[Prime@ Range@ 500, PrimeQ@ FromDigits[ IntegerDigits[#, 5], 9] &] (* Giovanni Resta, Sep 12 2019 *)

is(p,b=9,c=5)=isprime(vector(#d=digits(p,c),i,b^(#d-i))*d~)&&isprime(p) \\ Note: Code only valid for b > c.

A036952 Numbers whose binary expansion is a decimal prime.

Original entry on oeis.org

3, 5, 23, 47, 89, 101, 149, 157, 163, 173, 179, 185, 199, 229, 247, 253, 295, 313, 329, 331, 355, 367, 379, 383, 405, 425, 443, 453, 457, 471, 523, 533, 539, 565, 583, 587, 595, 631, 643, 647, 653, 659, 671, 675, 689, 703, 709, 755, 781, 785, 815, 841, 855

Offset: 1

Patrick De Geest, Jan 04 1999

A100051(f(a(n))) = 1 with f(x) = if x<2 then x else 10*f(floor(x/2)) + x mod 2. - Reinhard Zumkeller, Mar 31 2010

Primes in A007088. - N. J. A. Sloane, Feb 17 2023

			1 = 1_2 is not a prime.
2 = 10_2 is not OK because 10 = 2*5 is not a prime.
3 = 11_2 is OK because 11 is a prime.
4 = 100_2 is not OK because 100 = 4*25 is not a prime.
5 = 101_2 is OK because 101 is a prime.
7 = 111_2 is not OK because 111 = 3*37.
11 = 1011_2 is not OK because 1011 = 3*337.
313 = 100111001_2 is OK because 100111001 is prime.

Cf. A007088, A020449, A036953-A036964.

Union of A156059 and A065720.

A007088 := proc(n)
dgs := convert(n,base,2) ;
add(op(i,dgs)*10^(i-1),i=1..nops(dgs)) ;
end proc:
isA036952 := proc(n)
isprime( A007088(n)) :
end proc:
A036952 := proc(n)
if n =1 then
3;
else
for a from procname(n-1)+1 do
if isA036952(a) then
return a ;
end if;
end do:
end if;
end proc:
seq(A036952(n),n=1..80) ;
# R. J. Mathar, Mar 12 2010
A036952 := proc() if isprime(convert(n,binary)) then RETURN (n); fi; end: seq(A036952(), n=1..1000);  # K. D. Bajpai, Jul 04 2014

f[n_,k_]:=FromDigits[IntegerDigits[n,k]];lst={};Do[If[PrimeQ[f[n,2]],AppendTo[lst,n]],{n,7!}];lst (* Vladimir Joseph Stephan Orlovsky, Mar 12 2010 *)
NestList[NestWhile[# + 2 &, #, ! PrimeQ[FromDigits[IntegerDigits[#2, 2]]] &, 2] &, 3, 52] (* Jan Mangaldan, Jul 02 2020 *)

is(n)=my(v=binary(n));isprime(sum(i=1,#v,v[i]*10^(#v-i))) \\ Charles R Greathouse IV, Jun 28 2013

Entry revised by R. J. Mathar and N. J. A. Sloane, Mar 12 2010

A020472 Primes that contain digits 8 and 9 only.

Original entry on oeis.org

89, 8999, 89899, 89989, 98899, 98999, 99989, 888989, 898889, 989999, 998989, 8888989, 8889889, 8988989, 8989999, 8998889, 8999899, 9888889, 9889889, 9899999, 9989899, 9999889, 88888999, 88898989, 88989899, 89888989, 89889889, 89898889, 89999999, 98888989

Offset: 1

David W. Wilson

Or, primes with minimal digit 8.

Michael S. Branicky, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Vincenzo Librandi)
Index to entries about primes with digits in a given set

Cf. A020449 (digits 0 & 1), ..., A020471 (digits 7 & 9). - M. F. Hasler, Mar 18 2010

Select[Prime[Range[80000]], Min[IntegerDigits[#]] == 8 &] (* Zak Seidov, May 07 2005 *)
Flatten[Table[Select[FromDigits/@Tuples[{8, 9}, n], PrimeQ], {n, 8}]] (* Vincenzo Librandi, Jul 27 2012 *)

for(nd=1,9, p=vector(nd,i,10^(nd-i))~; forvec(v=vector(nd,i,[8+(i==nd),9]), isprime(v*p) && print1(v*p","))) \\ M. F. Hasler, Mar 18 2010

from sympy import isprime
from itertools import count, islice, product
def agen(): # generator of terms
    for d in count(2):
        for first in product("89", repeat=d-1):
            t = int("".join(first) + "9")
            if isprime(t): yield t
print(list(islice(agen(), 30))) # Michael S. Branicky, Nov 15 2022

Edited by N. J. A. Sloane, Jan 26 2008 at the suggestion of Lekraj Beedassy

A199325 Primes having only {0, 1, 5} as digits.

Original entry on oeis.org

5, 11, 101, 151, 1051, 1151, 1511, 5011, 5051, 5101, 5501, 10111, 10151, 10501, 11551, 15101, 15511, 15551, 50051, 50101, 50111, 50551, 51001, 51151, 51511, 51551, 55001, 55051, 55501, 55511, 100151, 100501, 100511, 101051, 101111, 101501, 110051, 110501, 115001, 115151, 150001, 150011, 150151, 150551

Offset: 1

M. F. Hasler, Nov 05 2011

Robert Israel, Table of n, a(n) for n = 1..10000
Index to entries about primes with digits in a given set

Cf. A020449 - A020472, A199326 - A199329, A061247, A199340 - A199349.

[p: p in PrimesUpTo(160000) | Set(Intseq(p)) subset [0, 1, 5]]; // Vincenzo Librandi, Apr 22 2014

N:= 10000: # to get the first N terms
count:= 0:
allowed:= {0,1,5}:
nallowed:= nops(allowed):
subst:= seq(i=allowed[i+1],i=0..nallowed-1):
for d from 0 while count < N do
  for x1 from 1 to nallowed-1 while count < N do
    for t from 0 to nallowed^d-1 while count < N do
      L:= subs(subst,convert(x1*nallowed^d+t,base,nallowed));
      X:= add(L[i]*10^(i-1),i=1..d+1);
      if isprime(X) then
          count:= count+1;
          A[count]:= X;
      fi
od od od:
seq(A[n],n=1..N); # Robert Israel, Apr 20 2014

Select[FromDigits/@Tuples[{0,1,5},6],PrimeQ] (* Harvey P. Dale, Jul 23 2021 *)

L=[0,1,5];for(d=1,6,u=vector(d,i,10^(d-i))~;forvec(v=vector(d,i,[1+(i==1 & !L[1]),#L]),ispseudoprime(t=vector(d,i,L[v[i]])*u)&print1(t",")))  /* see A199327 for a function a(n) */

A199329 Primes having only {0, 1, 9} as digits.

Original entry on oeis.org

11, 19, 101, 109, 191, 199, 911, 919, 991, 1009, 1019, 1091, 1109, 1901, 1999, 9001, 9011, 9091, 9109, 9199, 9901, 10009, 10091, 10099, 10111, 10909, 11119, 11909, 19001, 19009, 19919, 19991, 90001, 90011, 90019, 90191, 90199, 90901, 90911, 91009, 91019, 91099, 91199, 91909, 99109, 99119, 99191, 99901, 99991

Offset: 1

M. F. Hasler, Nov 05 2011

Alois P. Heinz, Table of n, a(n) for n = 1..10000
Index to entries about primes with digits in a given set

Cf. A020449 - A020472, A036953, A260044, A260267 - A260271, A199325 - A199327, A061247, A199340 - A199349.

Select[FromDigits/@Tuples[{0,1,9},5],PrimeQ] (* Harvey P. Dale, Dec 10 2016 *)

A199329(n=50,show=0,L=[0,1,9])={for(d=1,1e9,my(t,u=vector(d,i,10^(d-i))~);forvec(v=vector(d,i,[1+!(L[1]||(i>1&&iM. F. Hasler, Jul 25 2015

A235615 Primes whose base-5 representation also is the base-4 representation of a prime.

Original entry on oeis.org

2, 3, 13, 41, 43, 61, 181, 191, 263, 281, 283, 331, 383, 431, 443, 463, 641, 643, 661, 881, 911, 1063, 1091, 1291, 1303, 1531, 1693, 2083, 2143, 2203, 2293, 2341, 3163, 3181, 3191, 3253, 3343, 3593, 3761, 3931, 4001, 4093, 4391, 4691, 4793, 5011, 5393, 5413, 5441, 6301

Offset: 1

M. F. Hasler, Jan 13 2014

This sequence is part of the two-dimensional array of sequences based on this same idea for any two different bases b, c > 1. Sequence A235265 and A235266 are the most elementary ones in this list. Sequences A089971, A089981 and A090707 through A090721, and sequences A065720 - A065727, follow the same idea with one base equal to 10.

			Both 13 = 23_5 and 23_4 = 11 are prime.

Robert Price, Table of n, a(n) for n = 1..107268
M. F. Hasler, Primes whose base c expansion is also the base b expansion of a prime

Cf. A235474, A235265, A235266, A152079, A235461 - A235482, A065720 - A065727, A235394, A235395, A089971 ⊂ A020449, A089981, A090707 - A091924, A235615 - A235639. See the LINK for further cross-references.

is(p,b=4,c=5)=vecmax(d=digits(p,c))

forprime(p=1,3e3,is(p,5,4)&&print1(vector(#d=digits(p,4),i,5^(#d-i))*d~,",")) \\ To produce the terms, this is more efficient than to select them using straightforwardly is(.)=is(.,4,5)

cp's OEIS Frontend

A100580 Palindromic primes containing digits 0 and 1 only. (Palindromic terms in A020449.)

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A004022 Primes of the form (10^k - 1)/9. Also called repunit primes or repdigit primes.

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A089971 Primes whose decimal representation also represents a prime in base 2.

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A235265 Primes whose base-3 representation also is the base-2 representation of a prime.

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A235482 Primes whose base-5 representation is also the base-9 representation of a prime.

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A036952 Numbers whose binary expansion is a decimal prime.

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A020472 Primes that contain digits 8 and 9 only.

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