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 21-29 of 29 results.

A128049 Least number k>0 such that abs((3^k - (3-n)^k)/n) is prime, or 0 if no such prime exists.

Original entry on oeis.org

0, 2, 3, 2, 2, 3, 0, 3, 2, 2, 3, 2, 0, 2, 3, 0, 3, 2, 0, 2, 37, 0, 3, 2, 0, 2, 1153, 0, 83, 2, 0, 3, 11, 0, 3, 2, 0, 2, 3, 0, 557, 19, 0, 2, 3, 0, 7, 2, 0, 2, 631, 0, 5, 2, 0, 3, 3, 0, 239, 2, 0, 5, 3, 0, 3, 2, 0, 2, 317, 0, 3, 103, 0, 2, 7, 0, 3, 2, 0, 2, 43
Offset: 0

Views

Author

Alexander Adamchuk, Feb 12 2007

Keywords

Comments

a(-n) = A128033(n).
a(3*n) = 0 except a(3) = a(9) = 2.
All positive terms are primes.

Links

Crossrefs

Cf. A128033 (least number k>0 such that ((n+3)^k - 3^k)/n is prime), A028491 (numbers n such that (3^n - 1)/2 is prime).
Cf. A111010, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.

Programs

  • PARI
    a(n) = my(p=3); if(isprime(abs(n-6)), 2, if(n%3, while(!ispseudoprime((3^p-(3-n)^p)/n), p=nextprime(p+1)); p, 0)); \\ Jinyuan Wang, Nov 28 2020

Extensions

Name changed by Jinyuan Wang, Nov 28 2020

A173718 Numbers n such that (9^n - 2^n)/7 is prime.

Original entry on oeis.org

2, 3, 5, 13, 29, 37, 1021, 1399, 2137, 4493, 5521, 108553, 200807
Offset: 1

Views

Author

Robert Price, Dec 22 2012

Keywords

Comments

All terms are prime.
a(14) > 10^6.

Links

Crossrefs

Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.

Programs

  • Mathematica
    Select[ Prime[ Range[1, 100000] ], PrimeQ[ (9^# - 2^#)/7 ]& ]
  • PARI
    is(n)=ispseudoprime((9^n-2^n)/7) \\ Charles R Greathouse IV, Jun 06 2017

Extensions

a(12)-a(13) from Jon Grantham, Jul 29 2023

A128033 Least number k>0 such that ((n+3)^k - 3^k)/n is prime, or 0 if no such prime exists.

Original entry on oeis.org

0, 2, 13, 0, 3, 2, 0, 2, 3, 0, 7, 2, 0, 2, 3, 0, 73, 2, 0, 5, 3, 0, 3, 2, 0, 2, 3, 0, 3, 3, 0, 2, 5, 0, 3, 2, 0, 2, 401, 0, 3, 2, 0, 5, 5, 0, 3, 2, 0
Offset: 0

Views

Author

Alexander Adamchuk, Feb 11 2007

Keywords

Comments

All positive terms are primes.
a(50)-a(67) = {7, 0, 79, 2, 0, 2, 109, 0, 5, 5, 0, 2, 5, 0, 131, 2, 0, 2}. a(69)-a(121) = {0, 3, 19, 0, 2, 5, 0, 11, 2, 0, 13, 7, 0, 3, 2, 0, 3, 11, 0, 3, 19, 0, 2, 3, 0, 11, 2, 0, 2, 3, 0, 17, 2, 0, 2, 3, 0, 5, 2, 0, 3, 31, 0, 17, 5, 0, 47, 31, 0, 3, 3, 0, 2}.
a(49) > 10000. - Jinyuan Wang, Nov 28 2020

Crossrefs

Cf. A128049 (least number k>0 such that abs((3^k - (3-n)^k)/n) is prime), A028491, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.

Programs

  • PARI
    a(n) = my(p=2); if(n%3, while(!ispseudoprime(((n+3)^p-3^p)/n), p=nextprime(p+1)); p, 0); \\ Jinyuan Wang, Nov 28 2020

Formula

a(3*n) = 0.

A215487 Numbers k such that (7^k - 2^k)/5 is prime.

Original entry on oeis.org

3, 7, 19, 79, 431, 1373, 1801, 2897, 46997, 341063, 508867, 720497, 846913
Offset: 1

Views

Author

Robert Price, Aug 12 2012

Keywords

Comments

All terms are prime.
a(14) > 10^6.

Links

Crossrefs

Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.

Programs

  • Mathematica
    Select[ Prime[ Range[1, 300] ], PrimeQ[ (7^# - 2^#)/5 ]& ]
  • PARI
    is(n)=ispseudoprime((7^n-2^n)/5) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(10)-a(13) from Jon Grantham, Jul 29 2023

A224691 Numbers n such that (13^n - 4^n)/9 is prime.

Original entry on oeis.org

2, 5, 19, 109, 157, 8521, 26017, 26177
Offset: 1

Views

Author

Robert Price, Apr 15 2013

Keywords

Comments

All terms are prime.
a(9) > 10^5.

Crossrefs

Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032, A210506, A128347.

Programs

  • Mathematica
    Select[Prime[Range[1, 100000]], PrimeQ[(13^# - 4^#)/9]&]
  • PARI
    is(n)=ispseudoprime((13^n-4^n)/9) \\ Charles R Greathouse IV, Jun 13 2017

A228076 Numbers k such that (19^k - 4^k)/15 is prime.

Original entry on oeis.org

2, 7, 11, 31, 47, 139, 263, 769, 20551, 21491, 112247
Offset: 1

Views

Author

Robert Price, Aug 09 2013

Keywords

Comments

All terms are prime.
a(12) > 2*10^5.

Crossrefs

Cf. A224691, A128354, A128032.

Programs

  • Mathematica
    Select[Prime[Range[1, 100000]], PrimeQ[(19^# - 4^#)/15]&]
  • PARI
    is(n)=ispseudoprime((19^n-4^n)/15) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(11) from Robert Price, Mar 06 2021

A230139 Numbers n such that (17^n - 4^n)/13 is prime.

Original entry on oeis.org

3, 5, 7, 11, 31, 101, 887, 4861
Offset: 1

Views

Author

Robert Price, Oct 10 2013

Keywords

Comments

All terms are prime.
a(9) > 10^5.

Crossrefs

Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032, A210506, A128347, A128352, A225807.

Programs

  • Mathematica
    Select[Prime[Range[1, 100000]], PrimeQ[(17^# - 4^#)/13]&]
  • PARI
    is(n)=ispseudoprime((17^n-4^n)/13) \\ Charles R Greathouse IV, Jun 13 2017

A241921 Numbers k such that (15^k - 4^k)/11 is prime.

Original entry on oeis.org

2, 1097, 2243, 2857, 4357, 6803, 20747, 24571
Offset: 1

Views

Author

Robert Price, May 01 2014

Keywords

Comments

All terms are prime.
a(9) > 10^5.
a(1) is trivially prime, the remainder are probable primes.

Crossrefs

Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032, A210506, A128347, A225955, A062581.

Programs

  • Mathematica
    Select[Prime[Range[1, 100000]], PrimeQ[(15^# - 4^#)/11]&]
  • PARI
    is(n)=ispseudoprime((15^n-4^n)/11) \\ Charles R Greathouse IV, Jun 13 2017

A375620 Numbers k such that (20^k - 3^k)/17 is prime.

Original entry on oeis.org

2, 43, 1723, 2971, 3257, 12263, 38933
Offset: 1

Views

Author

William Dean, Aug 21 2024

Keywords

Comments

All terms must be prime.
a(8) > 10^5.

Examples

			a(1) = 2 corresponds to the prime number 23.

Links

Crossrefs

Cf. A028491, A057468, A128032, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.

Programs

  • PARI
    is(k) = ispseudoprime((20^k - 3^k)/17)
Previous Showing 21-29 of 29 results.

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