%I #24 Sep 22 2025 16:00:29

%S 8,88,688,4688,54688,554688,3554688,93554688,893554688,893554688,

%T 40893554688,40893554688,40893554688,70040893554688,870040893554688,

%U 1870040893554688,71870040893554688,871870040893554688

%N 2-automorphic numbers: final digits of 2*n^2 agree with n.

%C a(n) is the unique positive integer less than 10^n such that a(n) is divisible by 2^n and 2*a(n) - 1 is divisible by 5^n. - _Eric M. Schmidt_, Aug 18 2012

%H Eric M. Schmidt, <a href="/A030984/b030984.txt">Table of n, a(n) for n = 1..1000</a>

%H Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AutomorphicNumber.html">Automorphic Number</a>

%H <a href="/index/Ar#automorphic">Index entries for sequences related to automorphic numbers</a>

%H <a href="/index/Fi#final">Index entries for sequences related to final digits of numbers</a>

%o (SageMath) [crt(0, (5^n + 1)/2, 2^n, 5^n) for n in range(1, 1001)] # _Eric M. Schmidt_, Aug 18 2012

%K nonn,base

%O 1,1

%A _Eric W. Weisstein_