F(n) = f_n(10) f_n(x) : cyclotomic polynomial F( 1) = 9 = 3*3 F( 2) = 11 = prime F( 3) = 111 = 3*37 F( 4) = 101 = prime F( 5) = 11111 = 41*271 F( 6) = 91 = 7*13 F( 7) = 1111111 = 239*4649 F( 8) = 10001 = 73*137 F( 9) = 1001001 = 3*333667 F(10) = 9091 = prime F(11) = 11111111111 = 21649*513239 F(12) = 9901 = prime F(13) = 1111111111111 = 53*79*265371653 F(14) = 909091 = prime F(15) = 90090991 = 31*2906161 F(16) = 100000001 = 17*5882353 F(17) = 11111111111111111 = 2071723*5363222357 F(18) = 999001 = 19*52579 F(19) = 1111111111111111111 = prime F(20) = 99009901 = 3541*27961 F(21) = 900900990991 = 43*1933*10838689 F(22) = 9090909091 = 11*23*4093*8779 F(23) = 11111111111111111111111 = prime F(24) = 99990001 = prime F(25) = 100001000010000100001 = 21401*25601*182521213001 F(26) = 909090909091 = 859*1058313049 F(27) = 1000000001000000001 = 3*757*440334654777631 F(28) = 990099009901 = 29*281*121499449 F(29) = 11111111111111111111111111111 = 3191*16763*43037*62003*77843839397 F(30) = 109889011 = 211*241*2161 F(31) = 1111111111111111111111111111111 = 2791*6943319*57336415063790604359 F(32) = 10000000000000001 = 353*449*641*1409*69857 F(33) = 90090090090990990991 = 67*1344628210313298373 F(34) = 9090909090909091 = 103*4013*21993833369 F(35) = 900009090090909909099991 = 71*123551*102598800232111471 F(36) = 999999000001 = prime F(37) = 1111111111111111111111111111111111111 = 2028119*247629013*2212394296770203368013 F(38) = 909090909090909091 = prime F(39) = 900900900900990990990991 = prime F(40) = 9999000099990001 = 1676321*5964848081 F(41) = 11111111111111111111111111111111111111111 = 83*1231*538987*201763709900322803748657942361 F(42) = 1098900989011 = 7*127*2689*459691 F(43) = 1111111111111111111111111111111111111111111 = 173*1527791*1963506722254397*2140992015395526641 F(44) = 99009900990099009901 = 89*1052788969*1056689261 F(45) = 999000000999000999999001 = 238681*4185502830133110721 F(46) = 9090909090909090909091 = 47*139*2531*549797184491917 F(47) = 11111111111111111111111111111111111111111111111 = 35121409*316362908763458525001406154038726382279 F(48) = 9999999900000001 = prime F(49) = 1000000100000010000001000000100000010000001 = 505885997*1976730144598190963568023014679333 F(50) = 99999000009999900001 = 251*5051*78875943472201