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A306448 Pseudoprimes to base 9 that are not squarefree. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 24 18:11 EDT 2022. Contains 356949 sequences. (Running on oeis4.)