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 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

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