Question 848491
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Hi,
{{{S[n]=(n/2)(2*a[1]+ (n-1)d)}}}
{{{S[n]=( n/2)(1+n)}}} d = 1 and {{{2a[1] = 2}}}, {{{a[1] = 1}}}
{1, 2, 3, 4, 5, ....}  and {{{S[5]=( 5/2)(6)= 15}}}
 {{{a[5] = 5}}}