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 1-10 of 13 results. Next

A007350 Where the prime race 4k-1 vs. 4k+1 changes leader.

Original entry on oeis.org

3, 26861, 26879, 616841, 617039, 617269, 617471, 617521, 617587, 617689, 617723, 622813, 623387, 623401, 623851, 623933, 624031, 624097, 624191, 624241, 624259, 626929, 626963, 627353, 627391, 627449, 627511, 627733, 627919, 628013, 628427, 628937, 629371
Offset: 1

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Author

Keywords

Comments

The following references include some on the "prime race" question that are not necessarily related to this particular sequence. - N. J. A. Sloane, May 22 2006
Starting from a(12502) = A051025(27556) = 9103362505801, the sequence includes the 8th sign-changing zone predicted by C. Bays et al. The sequence with the first 8 sign-changing zones contains 194367 terms (see a-file) with a(194367) = 9543313015387 as its last term. - Sergei D. Shchebetov, Oct 13 2017

References

  • Ford, Kevin; Konyagin, Sergei; Chebyshev's conjecture and the prime number race. IV International Conference "Modern Problems of Number Theory and its Applications": Current Problems, Part II (Russian) (Tula, 2001), 67-91.
  • Granville, Andrew; Martin, Greg; Prime number races. (Spanish) With appendices by Giuliana Davidoff and Michael Guy. Gac. R. Soc. Mat. Esp. 8 (2005), no. 1, 197-240.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A156749 [sequence showing Chebyshev bias in prime races (mod 4)]. - Daniel Forgues, Mar 26 2009

Programs

  • Mathematica
    lim = 10^5; k1 = 0; k3 = 0; t = Table[{p = Prime[k], If[Mod[p, 4] == 1, ++k1, k1], If[Mod[p, 4] == 3, ++k3, k3]}, {k, 2, lim}]; A007350 = {3}; Do[ If[t[[k-1, 2]] < t[[k-1, 3]] && t[[k, 2]] == t[[k, 3]] && t[[k+1, 2]] > t[[k+1, 3]] || t[[k-1, 2]] > t[[k-1, 3]] && t[[k, 2]] == t[[k, 3]] && t[[k+1, 2]] < t[[k+1, 3]], AppendTo[A007350, t[[k+1, 1]]]], {k, 2, Length[t]-1}]; A007350 (* Jean-François Alcover, Sep 07 2011 *)
    lim = 10^5; k1 = 0; k3 = 0; p = 2; t = {}; parity = Mod[p, 4]; Do[p = NextPrime[p]; If[Mod[p, 4] == 1, k1++, k3++]; If[(k1 - k3)*(parity - Mod[p, 4]) > 0, AppendTo[t, p]; parity = Mod[p, 4]], {lim}]; t (* T. D. Noe, Sep 07 2011 *)

A038691 Indices of primes at which the prime race 4k-1 vs. 4k+1 is tied.

Original entry on oeis.org

1, 3, 7, 13, 89, 2943, 2945, 2947, 2949, 2951, 2953, 50371, 50375, 50377, 50379, 50381, 50393, 50413, 50423, 50425, 50427, 50429, 50431, 50433, 50435, 50437, 50439, 50445, 50449, 50451, 50503, 50507, 50515, 50517, 50821, 50843, 50853, 50855, 50857, 50859, 50861
Offset: 1

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Author

Keywords

Comments

Starting from a(27410) = 316064952537 the sequence includes the 8th sign-changing zone predicted by C. Bays et al back in 2001. The sequence with the first 8 sign-changing zones contains 419467 terms (see a-file) with a(419467) = 330797040309 as its last term. - Sergei D. Shchebetov, Oct 16 2017

Examples

			From _Jon E. Schoenfield_, Jul 24 2021: (Start)
a(n) is the n-th number m at which the prime race 4k-1 vs. 4k+1 is tied:
.
                             count
                           ----------
   m  p=prime(m)  p mod 4  4k-1  4k+1
  --  ----------  -------  ----  ----
   1       2         2       0  =  0    a(1)=1
   2       3        -1       1     0
   3       5        +1       1  =  1    a(2)=3
   4       7        -1       2     1
   5      11        -1       3     1
   6      13        +1       3     2
   7      17        +1       3  =  3    a(3)=7
   8      19        -1       4     3
   9      23        -1       5     3
  10      29        +1       5     4
  11      31        -1       6     4
  12      37        +1       6     5
  13      41        +1       6  =  6    a(4)=13
(End)
		

References

  • Stan Wagon, The Power of Visualization, Front Range Press, 1994, pp. 2-3.

Crossrefs

Cf. A156749; sequence showing Chebyshev bias in prime races (mod 4). - Daniel Forgues, Mar 26 2009

Programs

  • Mathematica
    Flatten[ Position[ FoldList[ Plus, 0, Mod[ Prime[ Range[ 2, 50900 ] ], 4 ]-2 ], 0 ] ]
  • PARI
    lista(nn) = {nbp = 0; nbm = 0; forprime(p=2, nn, if (((p-1) % 4) == 0, nbp++, if (((p+1) % 4) == 0, nbm++)); if (nbm == nbp, print1(primepi(p), ", ")););} \\ Michel Marcus, Nov 20 2016

A096447 Odd primes p such that the number of primes less than p that are congruent to 1 (mod 4) is equal to the number of primes less than p that are congruent to 3 (mod 4).

Original entry on oeis.org

3, 7, 19, 43, 463, 26839, 26861, 26879, 26891, 26903, 26927, 616783, 616799, 616841, 616849, 616877, 617039, 617269, 617369, 617401, 617429, 617453, 617471, 617479, 617521, 617537, 617587, 617689, 617717, 617723, 618439, 618547, 618619, 618643
Offset: 1

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Author

Yasutoshi Kohmoto, Aug 12 2004

Keywords

Comments

Assign the odd prime numbers to the rows of an array as follows:
Assign the first odd prime, prime(2) = 3, to row 0 (the top row).
For m > 2, assign prime(m) to the row immediately above or below the row to which prime(m-1) was assigned: above if prime(m-1) == 1 (mod 4), below otherwise.
The following array results:
row 0 (this sequence): 3, 7, 19, 43, 463, 26839, ...
row 1 (A096448): 5, 11, 17, 23, 31, 41, 47, 59, 67, 103, 127, ...
row 2 (A096451): 13, 29, 37, 53, 61, 71, 79, 101, 107, 113 ...
row 3: 73, 83, 97, 109, ...
row 4: 89, ...

Crossrefs

Programs

  • Mathematica
    lim = 10^5; k1 = 0; k3 = 0; p = 2; t = {}; Do[p = NextPrime[p]; If[k1 == k3, AppendTo[t, p]]; If[Mod[p, 4] == 1, k1++, k3++], {lim}]; t (* T. D. Noe, Sep 07 2011 *)

Formula

a(n) = A151800(A007351(n)), the next prime after A007351(n). - Joshua Zucker, May 03 2006

Extensions

More terms from Joshua Zucker, May 03 2006
"odd" added to definition by N. J. A. Sloane, Sep 09 2015

A051024 Values of n for which pi_{4,3}(p_n) - pi_{4,1}(p_n) = -1, where p_n is the n-th prime and pi_{m,a}(x) is the number of primes <= x which are congruent to a (mod m).

Original entry on oeis.org

2946, 50378, 50380, 50382, 50392, 50414, 50418, 50420, 50422, 50424, 50426, 50428, 50430, 50436, 50438, 50446, 50448, 50450, 50822, 50832, 50834, 50842, 50844, 50852, 50854, 50856, 50858, 50862, 50864, 50866, 50872, 50892, 50902
Offset: 1

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Author

Keywords

Comments

This is a companion sequence to A051025.
Starting from a(27556) = 316064952540 the sequence includes the 8th sign-changing zone predicted by C. Bays et al. The sequence with the first 8 sign-changing zones contains 418933 terms (see a-file) with a(418933) = 330797040308 as its last term. - Sergei D. Shchebetov, Oct 06 2017
We also discovered the 9th sign-changing zone, which starts from 2083576475506, ends with 2083615410040, and has 13370 terms with pi_{4,3}(p) - pi_{4,1}(p) = -1. This zone is considerably lower than predicted by M. Deléglise et al. in 2004. - Andrey S. Shchebetov and Sergei D. Shchebetov, Dec 30 2017
We also discovered the 10th sign-changing zone, which starts from 21576098946648, ends with 22056324317296, and has 481194 terms with pi_{4,3}(p) - pi_{4,1}(p) = -1. This zone is considerably lower than predicted by M. Deléglise et al. in 2004. - Andrey S. Shchebetov and Sergei D. Shchebetov, Jan 28 2018

Crossrefs

Cf. A156749 (Sequence showing Chebyshev bias in prime races (mod 4)). - Daniel Forgues, Mar 26 2009

Programs

  • Mathematica
    For[i=2; d=0, True, i++, d+=Mod[Prime[i], 4]-2; If[d==-1, Print[i]]]
    (* Second program: *)
    Position[Accumulate@ Array[Mod[Prime@ #, 4] - 2 &, 51000], -1][[All, 1]] (* Michael De Vlieger, Dec 30 2017 *)
  • Python
    from sympy import nextprime; a, p = 0, 2
    for n in range(2, 50917):
        p=nextprime(p); a += p%4-2
        if a == -1: print(n, end = ', ') # Ya-Ping Lu, Jan 18 2025

Extensions

Edited by Dean Hickerson, Mar 05 2002

A051025 Primes p for which pi_{4,3}(p) - pi_{4,1}(p) = -1, where pi_{m,a}(x) is the number of primes <= x which are congruent to a (mod m).

Original entry on oeis.org

26861, 616841, 616849, 616877, 617011, 617269, 617327, 617339, 617359, 617369, 617401, 617429, 617453, 617521, 617537, 617689, 617699, 617717, 622813, 622987, 623003, 623107, 623209, 623299, 623321, 623341, 623353, 623401, 623423, 623437
Offset: 1

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Author

Keywords

Comments

This is a companion sequence to A051024.
Starting from a(27556)=9103362505801 the sequence includes the 8th sign-changing zone predicted by C. Bays et al. The sequence with the first 8 sign-changing zones contains 418933 terms (see a-file) with a(418933)=9543313015309 as its last term. - Sergei D. Shchebetov, Oct 06 2017
We also discovered the 9th sign-changing zone, which starts from 64083080712569, ends with 64084318523021, and has 13370 terms with pi_{4,3}(p) - pi_{4,1}(p) = -1. This zone is considerably lower than predicted by M. Deléglise et al. in 2004. - Andrey S. Shchebetov and Sergei D. Shchebetov, Dec 30 2017
We also discovered the 10th sign-changing zone, which starts from 715725135905981, ends with 732156384107921, and has 481194 terms with pi_{4,3}(p) - pi_{4,1}(p) = -1. This zone is considerably lower than predicted by M. Deléglise et al. in 2004. - Andrey S. Shchebetov and Sergei D. Shchebetov, Jan 28 2018

Crossrefs

Cf. A156749 Sequence showing Chebyshev bias in prime races (mod 4). - Daniel Forgues, Mar 26 2009

Programs

  • Mathematica
    For[i=2; d=0, True, i++, d+=Mod[p=Prime[i], 4]-2; If[d==-1, Print[p]]]
    (* Second program: *)
    Prime@ Position[Accumulate@ Array[Mod[Prime@ #, 4] - 2 &, 51000], -1][[All, 1]] (* Michael De Vlieger, Dec 30 2017 *)
  • Python
    from sympy import nextprime; a, p = 0, 2
    while p < 623803:
        p=nextprime(p); a += p%4-2
        if a == -1: print(p, end = ', ')  # Ya-Ping Lu, Jan 18 2025

Extensions

Edited by Dean Hickerson, Mar 10 2002

A096449 Primes p such that the number of primes q, 5 <= q < p, congruent to 1 mod 3, is equal to the number of such primes congruent to 2 mod 3.

Original entry on oeis.org

5, 11, 17, 23, 41, 47, 83, 167, 227, 233, 608981812919, 608981812961, 608981813017, 608981813569, 608981813677, 608981813833, 608981813851, 608981813927, 608981813939, 608981813963, 608981814043, 608981814149, 608981814251, 608981814827
Offset: 1

Views

Author

Yasutoshi Kohmoto, Aug 12 2004

Keywords

Comments

First term prime(3) = 5 is placed on 0th row.
If prime(n-1) = +1 mod 3 is on k-th row then we put prime(n) on (k-1)-st row.
If prime(n-1) = -1 mod 3 is on k-th row then we put prime(n) on (k+1)-st row.
This process makes an array of prime numbers:
5, 11, 17, 23, 41, 47, 83, ... (this sequence)
7, 13, 19, 29, 37, 43, 53, 71, 79, 89, 101, .. (A096452).
31, 59, 67, 73, 97, ... (A096453)
61, ...

Crossrefs

Programs

  • Mathematica
    lst = {5}; p = 0; q = 0; r = 5; While[r < 10^9, If[ Mod[r, 3] == 2, p++, q++ ]; r = NextPrime@r; If[p == q, AppendTo[lst, r]; Print@r]]; lst (* Robert G. Wilson v, Sep 20 2009 *)

Formula

For n>1, a(n) = prime(A096629(n-1)+1) = A000040(A096629(n-1)+1). - Max Alekseyev, Sep 19 2009
a(n) = A151800(A098044(n)) = A007918(A098044(n)+1).

Extensions

More terms and better definition from Joshua Zucker, May 21 2006
Terms a(11) onward from Max Alekseyev, Feb 10 2011

A297447 Values of n for which pi_{8,5}(p_n) - pi_{8,1}(p_n) = -1, where p_n is the n-th prime and pi_{m,a}(x) is the number of primes <= x which are congruent to a (mod m).

Original entry on oeis.org

30733704, 30733708, 30733714, 30733726, 30733729, 30733733, 30733743, 30733762, 30733764, 30733777, 30733781, 30733796, 30733853, 30733857, 30733860, 30733866, 30733880, 30733887, 30733890, 30734262
Offset: 1

Views

Author

Andrey S. Shchebetov and Sergei D. Shchebetov, Dec 30 2017

Keywords

Comments

This is a companion sequence to A297448. The first two sign-changing zones were discovered by Bays and Hudson back in 1979. We discovered four additional zones starting from a(22794) = 186422420112. The full sequence with all 6 zones checked up to 5*10^14 contains 664175 terms (see a-file) with a(664175) = 6097827689926 as its last term.
This sequence was checked up to 10^15 and the 7th sign-changing zone starting from a(664176) = 27830993289634 and ending with a(850232)= 27876113171315 was found. - Andrey S. Shchebetov and Sergei D. Shchebetov, Jul 28 2018
The y-coordinate of prime(a(n)) on the Cartesian grid defined in A379643 is -1. - Ya-Ping Lu, Jan 08 2025

Crossrefs

Programs

  • Python
    from sympy import nextprime; p, r1, r5 = 1, 0, 0
    for n in range(1, 30734263):
        p = nextprime(p); r = p%8
        if r == 1: r1 += 1
        elif r == 5: r5 += 1
    if r in {1, 5} and r1 == r5 + 1: print(n, end = ', ')  # Ya-Ping Lu, Jan 08 2025

A373225 Primes p = prime(k) such that 0 = Sum_{j=1..k} T(k, j) where T(n, k) = K(prime(n), prime(k)) * K(prime(k), prime(n)) and K is the Kronecker symbol.

Original entry on oeis.org

2, 11, 23, 31, 47, 59, 67, 103, 127, 419, 431, 439, 467, 1259, 1279, 1303, 26947, 615883, 616787, 617051, 617059, 617087, 617647, 617731, 617819, 617879, 618463, 618559, 618587, 618671, 620467, 623867, 623879, 624199, 624271, 624311, 624319, 624331, 626887, 626987, 627071
Offset: 1

Views

Author

Peter Luschny, May 29 2024

Keywords

Comments

It appears that, apart from 1st term 2, this is a subsequence of A096448. - Michel Marcus, May 30 2024
For n > 2, the sequence is exactly those terms p in A096448 with p == 3 (mod 4); see linked proof. - Michael S. Branicky, May 30 2024

Examples

			The corresponding indices in A373224 start: 1, 5, 9, 11, 15, 17, 19, 27, 31, 81, 83, 85, 91, 205, 207, 213.
T(k, j) defined as in the name. 11 is a term because 11 = prime(5) and Sum_{j=1..5} T(k, j) = 1 + (-1) + 1 + (-1) + 0 = 0.
		

Crossrefs

Programs

  • Maple
    A := select(n -> A373224(n) = 0, [seq(1..500)]):
    seq(ithprime(a), a in A);

Extensions

a(17) onward from Michel Marcus, May 30 2024

A295354 Primes p for which pi_{8,7}(p) - pi_{8,1}(p) = -1, where pi_{m,a}(x) is the number of primes <= x which are congruent to a (mod m).

Original entry on oeis.org

192252423729713, 192252423730849, 192252423731231, 192252423731633, 192252423731663, 192252423731839, 192252423732311, 192252423769201, 192252423769361, 192252423769537, 192252423772649, 192252423772807, 192252423772847, 192252423774023, 192252423774079, 192252423774457, 192252423779257, 192252423782521, 192252423783263, 192252423783551
Offset: 1

Views

Author

Andrey S. Shchebetov and Sergei D. Shchebetov, Nov 20 2017

Keywords

Comments

This sequence is a companion sequence to A295353. The sequence with the first found pi_{8,7}(p_n) - pi_{8,1}(p_n) sign-changing zone contains 234937 terms (see a-file) with a(237937) = 192876135747311 as its last term. In addition, a(1) = A275939(8).

Crossrefs

A096450 Primes p such that the number of primes q, 7 <= q < p, congruent to 1 or 2 mod 5, is equal to the number of such primes congruent to 3 or 4 mod 5.

Original entry on oeis.org

7, 29, 37, 61, 89, 101, 107, 113, 131, 151, 181, 239, 251, 271, 397, 421, 443, 463, 479, 491, 503, 557, 569, 577, 601, 743, 757, 787, 857, 863, 881, 887, 1291, 1511, 1531, 1549, 1609, 1657, 1667, 1693, 1699, 1861, 1987, 1997, 2003, 2017, 2053, 2377, 2393
Offset: 1

Views

Author

Yasutoshi Kohmoto, Aug 12 2004

Keywords

Comments

First term prime(4) = 7 is placed on 0th row.
If prime(n-1) = 1 or 2 mod 5 is on k-th row then we put prime(n) on (k-1)-st row.
If prime(n-1) = -1 or -2 mod 5 is on k-th row then we put prime(n) on (k+1)-st row.
This process produces the following array of prime numbers:
31, 97, ... row -1
7, 29, 37, 61, 89, 101, ... row 0 (this sequence)
11, 17, 23, 41, 47, 59, 67, 83, ... row 1 (A096454)
13, 19, 43, 53, 71, 79, ... row 2 (A096455)
73, ...

Crossrefs

Extensions

More terms and better definition from Joshua Zucker, May 21 2006
Showing 1-10 of 13 results. Next