cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-5 of 5 results.

A020459 Primes that contain digits 2 and 7 only.

Original entry on oeis.org

2, 7, 227, 277, 727, 2777, 7727, 22277, 22727, 22777, 27277, 72227, 72277, 72727, 272227, 272777, 727777, 777277, 2227727, 2227777, 2272727, 2277727, 2727727, 2772227, 7272227, 7722277, 7727777, 7772777, 7777727, 22227277, 22272277
Offset: 1

Views

Author

David W. Wilson

Keywords

Links

Crossrefs

Cf. A000040, A284921, A329760.

Programs

  • Magma
    [p: p in PrimesUpTo(22272277) | Set(Intseq(p)) subset [2, 7]]; // Vincenzo Librandi, Jul 27 2012
  • Mathematica
    Flatten[Table[Select[FromDigits/@Tuples[{2,7},n],PrimeQ],{n,8}]] (* Vincenzo Librandi, Jul 27 2012 *)

A284920 Numbers with digits 2 and 4 only.

Original entry on oeis.org

2, 4, 22, 24, 42, 44, 222, 224, 242, 244, 422, 424, 442, 444, 2222, 2224, 2242, 2244, 2422, 2424, 2442, 2444, 4222, 4224, 4242, 4244, 4422, 4424, 4442, 4444, 22222, 22224, 22242, 22244, 22422, 22424, 22442, 22444, 24222, 24224, 24242, 24244, 24422, 24424
Offset: 1

Views

Author

Jaroslav Krizek, Apr 05 2017

Keywords

Comments

All terms are even.

Crossrefs

Cf. Numbers with digits 2 and k only for k = 0 - 1 and 3 - 9: A169965 (k = 0), A007931 (k = 1), A032810 (k = 3), this sequence (k = 4), A072961 (k = 5), A284632 (k = 6), A284921 (k = 7), A284922 (k = 8), A284923 (k = 9).

Programs

  • Magma
    [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {2, 4}]
  • Mathematica
    Flatten@ Array[FromDigits /@ Tuples[{2, 4}, #] &, 5] (* Michael De Vlieger, Apr 06 2017 *)

Formula

a(n) = 2 * A007931(n).

A284922 Numbers with digits 2 and 8 only.

Original entry on oeis.org

2, 8, 22, 28, 82, 88, 222, 228, 282, 288, 822, 828, 882, 888, 2222, 2228, 2282, 2288, 2822, 2828, 2882, 2888, 8222, 8228, 8282, 8288, 8822, 8828, 8882, 8888, 22222, 22228, 22282, 22288, 22822, 22828, 22882, 22888, 28222, 28228, 28282, 28288, 28822, 28828
Offset: 1

Views

Author

Jaroslav Krizek, Apr 05 2017

Keywords

Comments

All terms are even.

Crossrefs

Cf. Numbers with digits 2 and k only for k = 0 - 1 and 3 - 9: A169965 (k = 0), A007931 (k = 1), A032810 (k = 3), A284920 (k = 4), A072961 (k = 5), A284632 (k = 6), A284921 (k = 7), this sequence (k = 8), A284923 (k = 9).

Programs

  • Magma
    [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {2, 8}]
  • Mathematica
    Flatten@ Array[FromDigits /@ Tuples[{2, 8}, #] &, 5] (* Michael De Vlieger, Apr 06 2017 *)

Formula

a(n) = 2 * A032822(n).

A284923 Numbers with digits 2 and 9 only.

Original entry on oeis.org

2, 9, 22, 29, 92, 99, 222, 229, 292, 299, 922, 929, 992, 999, 2222, 2229, 2292, 2299, 2922, 2929, 2992, 2999, 9222, 9229, 9292, 9299, 9922, 9929, 9992, 9999, 22222, 22229, 22292, 22299, 22922, 22929, 22992, 22999, 29222, 29229, 29292, 29299, 29922, 29929
Offset: 1

Views

Author

Jaroslav Krizek, Apr 06 2017

Keywords

Crossrefs

Prime terms are in A020460.
Numbers with digits 2 and k only for k = 0 - 1 and 3 - 9: A169965 (k = 0), A007931 (k = 1), A032810 (k = 3), A284920 (k = 4), A072961 (k = 5), A284632 (k = 6), A284921 (k = 7), A284922 (k = 8), this sequence (k = 9).

Programs

  • Magma
    [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {2, 9}]
  • Mathematica
    Select[Range[30000],SubsetQ[{2,9},Sort[DeleteDuplicates[IntegerDigits[#]]]] &] (* Stefano Spezia, Aug 06 2025 *)

A285011 Numbers with digits 7 and 9 only.

Original entry on oeis.org

7, 9, 77, 79, 97, 99, 777, 779, 797, 799, 977, 979, 997, 999, 7777, 7779, 7797, 7799, 7977, 7979, 7997, 7999, 9777, 9779, 9797, 9799, 9977, 9979, 9997, 9999, 77777, 77779, 77797, 77799, 77977, 77979, 77997, 77999, 79777, 79779, 79797, 79799, 79977, 79979
Offset: 1

Views

Author

Jaroslav Krizek, Apr 08 2017

Keywords

Crossrefs

Prime terms are in A020471.
Numbers with digits 7 and k only for k = 0 - 6 and 8 - 9: A204094 (k = 0), A276039 (k = 1), A284921 (k = 2), A143967 (k = 3), A284971 (k = 4), A284380 (k = 5), A256292 (k = 6), A256340 (k = 8), this sequence (k = 9).

Programs

  • Magma
    [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {7, 9}];
  • Mathematica
    Flatten@ Table[FromDigits /@ Tuples[{7, 9}, n], {n, 5}] (* Giovanni Resta, Apr 10 2017 *)
  • PARI
    a(n,{p=[7,9]})={my(v=binary(n+1));fromdigits(vector(#v-1,i,p[2]*v[i+1]+p[1]*!v[i+1]))} \\ R. J. Cano, Apr 09 2017
  • Python
    def a(n): return int(bin(n+1)[3:].replace('0', '7').replace('1', '9'))
print([a(n) for n in range(1, 45)]) # Michael S. Branicky, Jul 09 2021
Showing 1-5 of 5 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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