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A181607 Numbers n with k digits such 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 (list; graph; refs; listen; history; text; internal format)
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^k-n 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

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Last modified June 27 15:07 EDT 2017. Contains 288790 sequences.