Каждое третье число в числе 2020. Например: в числе 10 каждое третье - это 3, 6 и 9.

3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60,63,66,69,72,75,78,81,84,87,90,93,96,99,102,105,108,111,114,117,120,123,126,129,134,135,138,141,144,147,150,153,156,159,161,164,167,170,173,176,179,181,184,187,190,193,196,199,201,204,207,210,213,216,219,221,224,227,230,233,236,239,242,245,248,251,254,257,260,263,266,269,272,275,278,281,284,287,290,293,296,299,301,304,307,310,313,316,319,321,327,330,333,336,339,342,345,348,351,354,357,360,363,366,369,372,375,378,381,384,387,390,393,396,399,401,404,407,410,413,416,419,421,427,430,433,436,439,442,445,448,451,454,457,460,463,466,469,472,475,478,481,484,487,490,493,496,499,501,504,507,510,513,516,519,521,527,530,533,536,539,542,545,548,551,554,557,560,563,566,569,572,575,578,581,584,587,590,593,596,599,601,604,607,610,613,616,619,621,627,630,633,636,639,642,645,648,651,654,657,660,663,666,669,672,675,678,681,684,687,690,693,696,699,701,704,707,710,713,716,719,721,727,730,733,736,739,742,745,748,751,754,757,760,763,766,769,772,775,778,781,784,787,790,793,796,799,801,804,807,810,813,816,819,821,827,830,833,836,839,842,845,848,851,854,857,860,863,866,869,872,875,878,881,884,887,890,893,896,899

... 2014,2017,2020