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aaaa202

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n1=1, n2=2, n3=4, n4=7, n5=11, n6=16, n7=22 ... i.e. the difference betweens two successive numbers grows with 1 as we move from (n_N-1, n_N) to (n_N,n_N+1).

Is there a closed form expression f(k) for this sequence, i.e. f(1)=n1, f(2)=n2, f(3)=n3 etc.

edit: So basically I have a sequence with I think what is called a recurence relation equal to:

x_n+1 = x_n+n

Can I find a closed form for this?