Question 1100246
1, 1, 2, 4, 6, 18, 21, 84, 88, 440, 445, 2670, 2676, 18732, 18739, 149912, 149920, 1349280, 1349289, 13492890, 13492900, 148421900, 148421911, 1781062932, 1781062944, 23153818272,

Multiply by 1, add 1, multiply by 2, add 2, etc. 

also see https://www.algebra.com/algebra/homework/Sequences-and-series/Sequences-and-series.faq.question.884472.html