Search a number
modest n.  and  undulating n.

First numbers that belong to both sets:

515, 545, 818, 10101, 20202, 30303, 40404, 50505, 51515, 54545, 60606, 70707, 80808, 81818, 90909, 101010, 121212, 131313, 141414, 151515, 161616, 171717, 181818, 191919, 202020, 212121, 232323, 242424, 252525, 262626, 272727, 282828, 292929, 303030, 313131, 323232, 343434, 353535, 363636, 373737, 383838, 393939, 404040, 414141, 424242, 434343, 454545, 464646, 474747, 484848, 494949, 505050, 515151, 525252, 535353, 545454, 565656, 575757, 585858, 595959, 606060, 616161, 626262, 636363, 646464, 656565, 676767, 686868, 696969, 707070, 717171, 727272, 737373, 747474, 757575, 767676, 787878, 797979, 808080, 818181, 828282, 838383, 848484, 858585, 868686, 878787, 898989, 909090, 919191, 929292, 939393, 949494, 959595, 969696, 979797, 989898, 1010101, 2020202, 2121212, 2727272, 3030303, 4040404, 4242424, 5050505, 5151515, 5252525, 5454545, 5757575, 6060606, 6363636, 7070707, 8080808, 8181818, 8484848, 9090909, 10101010, 12121212, 13131313, 14141414, 15151515, 16161616, 17171717, 18181818, 19191919, 20202020, 21212121, 23232323, 24242424, 25252525, 26262626, 27272727, 28282828, 29292929, 30303030, 31313131, 32323232, 34343434, 35353535, 36363636, 37373737, 38383838, 39393939, 40404040, 41414141, 42424242, 43434343, 45454545, 46464646, 47474747, 48484848, 49494949, 50505050, 51515151, 52525252, 53535353, 54545454, 56565656, 57575757, 58585858, 59595959, 60606060, 61616161, 62626262, 63636363, 64646464, 65656565, 67676767, 68686868, 69696969, 70707070, 71717171, 72727272, 73737373, 74747474, 75757575, 76767676, 78787878, 79797979, 80808080, 81818181, 82828282, 83838383, 84848484, 85858585, 86868686, 87878787, 89898989, 90909090, 91919191, 92929292, 93939393, 94949494, 95959595, 96969696, 97979797, 98989898, 101010101, 202020202, 212121212, 272727272, 303030303, 404040404, 424242424, 505050505, 515151515, 525252525, 545454545, 575757575, 606060606, 636363636, 707070707, 808080808, 818181818, 848484848, 909090909, 1010101010, 1212121212, 1313131313, 1414141414, 1515151515, 1616161616, 1717171717, 1818181818, 1919191919.