login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A306449 Pseudoprimes to base 10 that are not squarefree. 2
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 (list; graph; refs; listen; history; text; internal format)
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 A100681 A043044

Adjacent sequences:  A306446 A306447 A306448 * A306450 A306451 A306452

KEYWORD

nonn

AUTHOR

Jianing Song, Feb 16 2019

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 9 17:13 EDT 2022. Contains 356026 sequences. (Running on oeis4.)