%I
%S 0,2,7,57,182,1068,1068,32318,110443,280182,3626068,23157318,
%T 120813568,123327057,1097376068,11109655182,49925501068,355101282318,
%U 355101282318,3459595983307,15613890344818,110981321985443
%N a(n) is smallest number such that a(n)^2 + 1 is divisible by 5^n.
%H Zak Seidov, <a href="/A034939/b034939.txt">Table of n, a(n) for n = 0..100</a>
%F a(n) = min(A048898(n), A048899(n)).
%t b=2; n5=5; jo=Join[{0,b}, Table[n5=5*n5; b=PowerMod[b,5,n5]; b=Min[b,n5b], {99}]] (* _Zak Seidov_, Nov 04 2011 *)
%t Table[x/.FindInstance[Mod[x^2+1,5^n]==0,x,Integers][[1]],{n,0,25}] (* _Harvey P. Dale_, Jul 04 2017 *)
%o (PARI) b(n)=if(n<2,2,b(n1)^5)%5^n; a(n)=min(b(n),5^nb(n))
%Y Cf. A034935, A199206.
%K nonn,nice,easy
%O 0,2
%A _N. J. A. Sloane_.
%E More terms from _Michael Somos_
