Question 865593: Write a recursive formula for the following sequence: 7, 10, 21, 30, 63, 90, 189, 270
Answer by richwmiller(17219)   (Show Source):
You can put this solution on YOUR website! 7, 10, 21, 30, 63, 90, 189, 270, 567, 810, 1701, 2430, 5103, 7290, 15309, 21870, 45927, 65610, 137781, 196830, 413343, 590490, 1240029, 1771470, 3720087, 5314410, 11160261, 15943230, 33480783, 47829690, 100442349, 143489070, 301327047, 430467210, 903981141, 1291401630, 2711943423, 3874204890, 8135830269, 11622614670, 24407490807, 34867844010, 73222472421, 104603532030, 219667417263, 313810596090, 659002251789, 941431788270, 1977006755367, 2824295364810, 5931020266101, 8472886094430, 17793060798303, 25418658283290, 53379182394909, 76255974849870, 160137547184727, 228767924549610, 480412641554181, 686303773648830, ...
7+3^1=10
3^1*7=21
3^2+7*3^1=30
7*3^2=63
or
3^3+3^1*7=90
7*3^3=189
(-7-10z)/(3z^2-1)
or
An = 1/2 3^(n/2-3/2)(21-21(-1)^n+10sqrt(3)+10 (-1)^n sqrt(3))
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