

A181607


Numbers n with k digits such that n^2 == 1 (mod 10^k).


2



1, 9, 49, 51, 99, 249, 251, 499, 501, 749, 751, 999, 1249, 3751, 4999, 5001, 6249, 8751, 9999, 18751, 31249, 49999, 50001, 68751, 81249, 99999, 218751, 281249, 499999, 500001, 718751, 781249, 999999, 4218751, 4999999, 5000001, 5781249, 9218751
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OFFSET

1,2


COMMENTS

Least term of n digits: 1, 49, 249, 1249, 18751, 218751, 4218751, ..., .
If n of k digits is present then 10^kn is present.
The union of A002283, A198971, A199685, A224473, A224474, A224475, and A224476 (except that this sequence omits 0, 4, and 6).  Eric M. Schmidt, Jan 26 2016


LINKS

Eric M. Schmidt, Table of n, a(n) for n = 1..1000


MATHEMATICA

Table[ Select[ Range[10^(k  1), 10^k  1], Mod[ #^2, 10^k] == 1 &], {k, 7}] // Flatten


CROSSREFS

Cf. A007185, A016090, A033819.
Sequence in context: A249780 A140891 A072461 * A012260 A262537 A133478
Adjacent sequences: A181604 A181605 A181606 * A181608 A181609 A181610


KEYWORD

base,easy,nonn


AUTHOR

Robert G. Wilson v, Nov 01 2010


STATUS

approved



