A306449 Pseudoprimes to base 10 that are not squarefree.

9, 99, 657, 909, 1233, 11169, 13833, 19503, 20961, 23661, 51291, 69921, 90009, 99297, 109737, 139329, 203841, 237169, 256059, 321201, 339021, 346473, 460251, 475641, 686169, 760761, 927081, 1080801, 1621089, 1679931, 3100833, 3316941, 3845601, 3846051, 3942657, 4095081, 4281057

Offset

1,1

Comments

Numbers k that are not squarefree and satisfy 10^(k-1) == 1 (mod k).

Any term is divisible by the square of a base-10 Wieferich prime (A045616 = {3, 487, 56598313, ...}).

Intersection of A005939 and A013929.

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Prog

(PARI) for(n=1, 10^6, if(Mod(10, 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), A306448 (b=9), this sequence (b=10).

Cf. also A045616, A005939, A013929.

Sequence in context: A147829 A116274 A116286 * A160946 A359078 A100681

Adjacent sequences: A306446 A306447 A306448 * A306450 A306451 A306452

Keyword

nonn

Author

Jianing Song, Feb 16 2019

Status

approved