Write down the next term in this sequence: -1 3 11 23 39
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Is it OK if I explain it before I write down the next term ?

-1  ___  3  ___  11  ___  23  ___  39  ___  (   )

The first blank is . . . . . " + 4 = " .

The second blank is . . " + 8 = " .

The third blank is . . . .  " + 12 = " . 

The fourth blank is . . . " + 16 = " .

So the fifth blank is . . . " + 20 = "  and the next number is  59 .