Question

which number will replace the question mark(?) in the series 1,3 10 ,24,64, 129,? ,777

Answer 1

i think the question is wrong in place of 24 there should be 21 because then the sequence will be like

if you multiply odd numbers with 2 and then add 1 you will get the number next to it for example

1*2+1 = 3 (here the number which is in odd place is 1 and the next to it with this method is correct )

but what about the number which is in even place so to get the number next to it just multiply the number with three and add 1. for example

3*3+1 = 10

so the ? came in odd(7) position so to calculate we have to use 129 which is in even place so for even place multiply the number with 3 and add 1. so we get
129*3+1 = 388

now to verify whether it is correct or not we would calculate the number next to it
so 388 is in odd place so to calculate the next to it we will multiply 388 with 3 and then add 1. That is
388*2+1
776+1
777 so our answer is correct

hope it helps