A273987 -id:A273987 - cp's OEIS frontend

A343914 Riesel problem in base 3: a(n) is the smallest k >= 0 such that (2n)3^k-1 is prime, or -1 if no such k exists.

1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 2, 0, 2, 1, 0, 0, 1, 1, 0, 2, 0, 0, 1, 0, 1, 2, 0, 1, 1, 0, 0, 1, 1, 0, 3, 0, 0, 1, 1, 0, 3, 0, 1, 1, 0, 2, 1, 2, 0, 3, 0, 0, 1, 0, 0, 3, 0, 1, 1, 1, 2, 3, 9, 0, 1, 0, 1, 2, 0, 0, 2, 1, 6, 1, 0, 0, 1, 1, 0, 1, 3, 0, 2, 0, 1, 3, 0

Offset: 1

Felix Fröhlich, May 04 2021

sign

31532322469 (A273987(3)/2) is the smallest n such that a(n) = -1.

			For n = 11: (2*11)*3^k-1 is prime for k = 2, with 2 being the smallest such k, so a(11) = 2.

Wikipedia, Riesel number

Cf. A040081 (base 2), A273987.

a(n) = for(k=0, oo, if(ispseudoprime((2*n)*3^k-1), return(k)))

A345403 Riesel problem in base 5: a(n) is the smallest k >= 0 such that (2n)5^k - 1 is prime, or -1 if no such k exists.

Original entry on oeis.org

4, 0, 0, 0, 3, 0, 0, 1, 0, 0, 1, 0, 4, 1, 0, 0, 163, 1, 0, 1, 0, 0, 1, 0, 2, 5, 0, 2, 7, 0, 0, 5, 5, 0, 1, 0, 0, 1, 1, 0, 1, 0, 2058, 1, 0, 26, 5, 1, 0, 1, 0, 0, 3, 0, 0, 3, 0, 32, 17, 1, 2, 1, 3, 0, 3, 0, 8, 21, 0, 0, 1, 1, 4, 1, 0, 0, 1, 4, 0, 7, 1, 0, 1, 0

Offset: 1

Felix Fröhlich, Jun 18 2021

sign

a(346802/2) = a(173401) = -1 (see A273987).

			For n = 5: 10*5^k - 1 is composite for k = 0, 1, 2 and prime for k = 3. Since 3 is the smallest such k, a(5) = 3.

Joe O, Project Description, Mersenne forum.
Reggie, Welcome to the Sierpinski/Riesel Base 5 Project, PrimeGrid forum.
Wikipedia, Riesel number

Cf. A040081 (base 2), A343914 (base 3), A250205 (base 6).

Cf. A273987.

a(n) = for(k=0, oo, if(ispseudoprime((2*n)*5^k-1), return(k)))

cp's OEIS Frontend

A343914 Riesel problem in base 3: a(n) is the smallest k >= 0 such that (2n)3^k-1 is prime, or -1 if no such k exists.

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A345403 Riesel problem in base 5: a(n) is the smallest k >= 0 such that (2n)5^k - 1 is prime, or -1 if no such k exists.

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cp's OEIS Frontend

A343914 Riesel problem in base 3: a(n) is the smallest k >= 0 such that (2*n)*3^k-1 is prime, or -1 if no such k exists.

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A345403 Riesel problem in base 5: a(n) is the smallest k >= 0 such that (2*n)*5^k - 1 is prime, or -1 if no such k exists.

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A343914 Riesel problem in base 3: a(n) is the smallest k >= 0 such that (2n)3^k-1 is prime, or -1 if no such k exists.

A345403 Riesel problem in base 5: a(n) is the smallest k >= 0 such that (2n)5^k - 1 is prime, or -1 if no such k exists.