Number Puzzle #68

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Actually this is a GP with first element as 1 and variable factor. where the factor comes from this series

1, 3, 7, 13.

Tn = Tn-1 + 2^(n-1);

T1 = 1;

T2 = T1 + 2^(2-1)= 1 + 2 = 3;

T3 = T2 + 2^(3-1) = 3 + 4 = 7;

T4 = T3 + 2^(4-1) = 7 + 6 = 13

nth number in GP = first number * (10)(Tn-1 in series);

First Element in GP = 1;

Second Element in GP(i.e. n = 2) = 1*10*(T1 in series); = 10

Third element in GP(i.e. n =3) = 1*10*(T2 in series) = 1*10*3 = 30

Fourth element in GP (i.e. n =4) = 1*10*(T3 in series) = 1*10*7 = 70

Fifth element in GP (i.e. n =5) = 1*10*(T4 in series) = 1*10*13 = 130

Thus the missing number here is 70.