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 1-3 of 3 results.

A089318 Smallest prime of the form an n-th power followed by digit 1.

Original entry on oeis.org

31, 41, 271, 811, 77761, 641, 21871, 16796161, 196831, 259374246011, 19773267431, 40961, 9688901040700000000000001, 163841, 1368800680154120519681, 1214395310965942517761, 58744031063604200188795536431, 3874204891, 2748779069441, 1757494343868923397049845066579063588307980412147890120011
Offset: 1

Views

Author

Amarnath Murthy, Nov 03 2003

Keywords

Examples

			a(4) = 811 is the prime which is the concatenation of 3^4 and 1. 161 is not a prime.

Crossrefs

Cf. A089319.

Programs

  • PARI
    a(n) = my(k=2); while (!isprime(10*k^n+1), k++); 10*k^n+1; \\ Michel Marcus, Mar 08 2025

Extensions

More terms from David Wasserman, Sep 09 2005
Missing a(1) inserted and more terms from Michel Marcus, Mar 08 2025

A381793 Smallest k>1 such that 10*k^(5*2^n)+1 is prime.

Original entry on oeis.org

6, 11, 649, 792, 1034, 12386, 21813, 87318, 35387, 207339, 67958
Offset: 0

Views

Author

Jakub Buczak, Mar 07 2025

Keywords

Examples

			a(0) = 6, because 10*6^(5*2^0)+1 equals 77761 which is prime.

Crossrefs

Cf. A020714, A089319.
Cf. A381815.

Programs

  • Python
    from sympy import isprime
from itertools import count
def a(n): return next(k for k in count(2) if isprime(k**(5*(2**n)) * 10 + 1))

Extensions

a(7)-a(10) from Michael S. Branicky, Mar 07 2025

A381815 Smallest k>1 such that 10*k^(3*2^n)+1 is prime.

Original entry on oeis.org

3, 2, 2, 2, 138, 24, 695, 107, 250, 404, 4657, 2185, 27931
Offset: 0

Views

Author

Jakub Buczak, Mar 07 2025

Keywords

Examples

			a(0) = 3, because 10*3^(3*2^0)+1 equals 271 which is prime.
a(1) = 2, because 10*2^(3*2^1)+1 equals 641 which is prime.

Crossrefs

Cf. A007283, A002254, A089319.
Cf. A381793.

Programs

  • Python
    from sympy import isprime
from itertools import count
def a(n): return next(k for k in count(2) if isprime(k**(3*(2**n)) * 10 + 1))

Extensions

a(10)-a(11) from Michael S. Branicky, Mar 07 2025
a(12) from Georg Grasegger, Apr 15 2025
Showing 1-3 of 3 results.

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

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