A306448 Pseudoprimes to base 9 that are not squarefree.

4, 8, 28, 52, 121, 364, 532, 616, 1036, 1288, 3052, 3751, 4376, 4636, 4961, 5356, 6364, 7381, 8744, 11011, 11476, 12124, 15964, 19096, 19684, 21196, 21736, 24388, 26596, 29161, 31876, 32791, 37576, 40132, 45676, 47972, 53092, 61831, 67276, 72136, 80476, 80956, 86296

Offset

1,1

Comments

Numbers k that are not squarefree and satisfy 9^(k-1) == 1 (mod k).

Any term is divisible by the square of a base-9 Wieferich prime ({2} U {base-3 Wieferich primes} = {2} U A014127 = {2, 11, 1006003, ...}).

Intersection of A020138 and A013929.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Prog

(PARI) for(n=1, 10^5, if(Mod(9, n)^(n-1)==1 && !issquarefree(n), print1(n, ", ")))

Crossrefs

Pseudoprimes to base b that are not squarefree: A158358 (b=2), A244065 (b=3), A243010 (b=5), A243089 (b=7), A243090 (b=8), this sequence (b=9), A306449 (b=10).

Cf. also A014127, A020138, A013929.

Sequence in context: A338429 A117864 A020138 * A090083 A034515 A189546

Adjacent sequences: A306445 A306446 A306447 * A306449 A306450 A306451

Keyword

nonn

Author

Jianing Song, Feb 16 2019

Status

approved