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%I #9 Aug 09 2021 01:33:08
%S 1,19,361,6859,80161,130321,142253,231059,1523059,1555207,2476099,
%T 2702807,4390121,28938121,29548933,47045881,51353333,83412299,
%U 188190383,338199259,549824299,561429727,600165407,893871739,974837921
%N Numbers k that divide 10^k + 9^k.
%t Select[ Range[ 10^9 ], Mod[ PowerMod[ 10, #, # ] + PowerMod[ 9, #, # ], # ] == 0 & ]
%K nonn
%O 1,2
%A _David W. Wilson_