What is the missing number in this sequence? 1,2,3,5,_,13,21,_

Question

I need help with an application question. Please help!

Answer 1

Given series is 1,2,3,5,_,13,21,_

Pattern of given series is just add the natural numbers in order two times to previous number.

First number is 1.

Second number 1+1 = 2

Third number    2+1 = 3

Fourth number  3+2 = 5

Fifth number     5+2 = 7

Next number    7+3 = 10

Next number   10+3 = 13

Next number   13+4 = 17

Next number  17+4 = 21

Next number  21+5 = 26

Missing numbers are 7,26.