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an+1 =an + 2n, a0 = 3. a100.
3.. {an} :
an+2 = 3an - 2 an+1; a0 = -1, a2.= 2 a6. a11
4. :
(3,5,12,15,16,20); (2,3,4,6,8,9,10,11,12,13,18).
5. {an} :
an+1 =an + n2; a0 = 0. a5. a150.
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10. {an} :
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