sequence answer for 3, 12, 21, 30, 39

Looks like a simple arithmetic progression with each term 9 more than the previous one. The n'th term could be written as: 3+9*(n-1) (where n≥1)

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The difference is 9 each time so part of it will be 9n

the first one is 9*1-6

the second is 9*2-6 etc

so

Tn=9n-6

( this is the same as Alan's answer)

find the next three terms in the sequence 3,12,21,30

39,48,57 LIKE A BOSS!