The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A178814 (n^(p-1) - 1)/p^2 mod p, where p is the first prime that divides (n^(p-1) - 1)/p. 1
 0, 487, 4, 974, 1, 30384, 1, 1, 0, 2, 46, 1571, 1, 17, 24160, 855, 0, 4, 1, 189, 1, 5, 11, 1, 0, 0, 1, 0, 1, 3, 2, 3, 0, 19632919407, 1, 60768, 1, 11, 1435, 8, 0, 0, 2, 2, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS (n^(p-1) - 1)/p^2 mod p, where p is the first prime such that p^2 divides n^(p-1) - 1. See references and additional comments, links, and cross-refs in A001220 and A039951. LINKS Wikipedia, Generalized Wieferich primes FORMULA a(n) = (n^(p-1) - 1)/p^2 mod p, where p = A039951(n). a(n) = k mod 2, if n = 4k+1. a(prime(n)) = A178813(n). EXAMPLE The first prime p that divides (3^(p-1) - 1)/p is 11, so a(3) = (3^10 - 1)/11^2 mod 11 = 488 mod 11 = 4. CROSSREFS a(2) = A178812(1) = A178813(1). Cf. A001220, A039951, A174422. Sequence in context: A179428 A252076 A178813 * A178812 A124667 A142540 Adjacent sequences:  A178811 A178812 A178813 * A178815 A178816 A178817 KEYWORD hard,more,nonn AUTHOR Jonathan Sondow, Jun 17 2010 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified January 17 12:38 EST 2020. Contains 330958 sequences. (Running on oeis4.)