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.

Previous Showing 11-13 of 13 results.

A090083 Even pseudoprimes to base 9.

Original entry on oeis.org

4, 8, 28, 52, 286, 364, 532, 616, 946, 1036, 1288, 2806, 2926, 3052, 4376, 4636, 5356, 6364, 8744, 8866, 11476, 12124, 15964, 17446, 19096, 19684, 21196, 21736, 24046, 24388, 26596, 31876
Offset: 1

Views

Author

Labos Elemer, Nov 25 2003

Keywords

Links

Crossrefs

Cf. A020138.
Cf. A006935, A130433, A090082, A090084, A090085, A130434, A130435, A130436, A130438, A130439, A130440, A130441, A130442, A130443.

Programs

  • Mathematica
    Do[s=Mod[ -1+9^(n-1), n]; If[Equal[s, 0]&&!PrimeQ[n]&&EvenQ[n], Print[n]], {n, 1, 1000000}]
  • PARI
    is(n)=Mod(9, n)^(n-1)==1&&!isprime(n)&&n%2==0 \\ Charles R Greathouse IV, Apr 12 2012
  • PARI
    p=2; forprime(q=3, 1e8, forstep(n=p+1, q-1, 2, if(Mod(9, n)^(n-1)==1, print1(n", "))); p=q) \\ Charles R Greathouse IV, Apr 12 2012

A130437 Even pseudoprimes to base 19.

Original entry on oeis.org

6, 18, 906, 5466, 257302, 825366, 1880082, 6637546, 6765826, 8936722, 9483706, 34087054, 51914026, 54806454, 57663334, 57819882, 67372378, 91835206, 98963734, 102985926, 117697186, 134457346, 143888806, 172530646, 206623266
Offset: 1

Views

Author

Alexander Adamchuk, May 26 2007

Keywords

Links

Crossrefs

Cf. A020147 = Pseudoprimes to base 19. Cf. A006935 = Even pseudoprimes (or primes) to base 2: n divides 2^n - 2, n even. Cf. A130433 = Even pseudoprimes to base 3. Cf. A090082 = Even pseudoprimes to base 5. Cf. A090083, A090084, A090085. Cf. A130434, A130435, A130436, A130438, A130439, A130440, A130441, A130442, A130443.
Cf. A020147, A006935, A130433, A090082, A090083, A090084, A090085, A130434, A130435, A130436, A130438, A130439, A130440, A130441, A130442, A130443.

Programs

  • Mathematica
    lst = {}; Do[ If[ PowerMod[19, 2n - 1, 2n] == 1, AppendTo[lst, 2n]], {n, 2, 2*10^9}]; lst (* Robert G. Wilson v, Jun 01 2007 *)
  • PARI
    is(k) = k > 2 && !(k % 2) &&  Mod(19, k)^(k-1) == 1; \\ Amiram Eldar, Sep 29 2024

Extensions

More terms from Robert G. Wilson v, Jun 01 2007

A108162 Least even pseudoprime > p to base p, where p = prime(n).

Original entry on oeis.org

161038, 286, 124, 16806, 70, 244, 1228, 906, 154, 52, 66, 66, 344, 526974, 506, 286, 946, 130, 154, 370, 276, 2626, 1558, 19126, 176, 190, 946, 742, 186, 176, 3486, 190, 148, 246, 412, 10930, 186, 186, 3818, 14444, 1246, 316, 286, 276, 532, 426, 310, 246
Offset: 1

Views

Author

Alexander Adamchuk, May 26 2007

Keywords

Comments

Some numbers appear as a multiple terms in a(n). For example, a(n) = 946 for n = {17,27,64,66,73,75,97,113,114,117,128,139,143,152,153,155} for corresponding prime p = {59,103,311,317,367,379,509,617,619,643,719,797,823,881,883,907}. There are some twin terms such that a(n) = a(n+1). For example, a(11) = a(12) = 66, a(37) = a(38) = 186, a(113) = a(114) = 946, a(152) = a(153) = 946, a(227) = a(228) = 2626.
The indices of records are 1, 14, 354, 549, 1302, 2679, 3743, 3998, 4627, 6880, ... with record values of 161038, 526974, 1234806, 1893126, 1930546, 3347398, 3860962, 5073706, 6376126, 61161946, ... - Amiram Eldar, Sep 10 2019

Links

Crossrefs

Cf. A006935 (Even pseudoprimes (or primes) to base 2: n divides 2^n - 2, n even).
Cf. A130433, A090082, A130434, A090084, A130435, A130436, A130437, A130438, A130439, A130440, A130441, A130442, A130443.

Programs

  • Mathematica
    a[n_] := Module[{p = Prime[n]}, k = p+1; If[OddQ[k], k++]; While[GCD[p, k] != 1 || PowerMod[p, k, k] != p, k+=2]; k]; Array[a, 100] (* Amiram Eldar, Sep 10 2019 *)
Previous Showing 11-13 of 13 results.

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