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%I #16 Jan 21 2019 19:01:55
%S 2,5,10,17,18,21,28,37,40,49,50,57,58,61,68,71,80,81,88,89,92,101,104,
%T 113,120,121,124,131,140,143,150,151,158,167,176,177,184,187,194,197,
%U 206,207,208,211,218,227,228,231,238,247,250,259,260,261,268,271,280
%N a(n) = Sum_{i=1..n} {last digit of prime(i)}.
%C Asymptotically, a(n) ~ 5n by Dirichlet's theorem. - _Charles R Greathouse IV_, Sep 28 2008
%e a(1) = 2;
%e a(2) = 2 + 3 = 5;
%e a(3) = 2 + 3 + 5 = 10;
%e a(4) = 2 + 3 + 5 + 7 = 17;
%e a(5) = 2 + 3 + 5 + 7 + 1(1) = 2 + 3 + 5 + 7 + 1 = 18.
%t f[n_] := Sum[ Mod[ Prime[i], 10], {i, n}]; Array[ f, 60] (* _Robert G. Wilson v_, Dec 22 2004 *)
%t Rest@ FoldList[Plus, 0, Mod[Prime@ Range@ 60, 10]] (* _Robert G. Wilson v_, Jan 16 2011 *)
%o (PARI) sum(k=1,n,prime(k)%10) \\ _Charles R Greathouse IV_, Sep 28 2008
%Y Partial sums of A007652.
%K nonn,base,easy
%O 1,1
%A _Jorge Coveiro_, Dec 22 2004
%E Corrected and extended by _Robert G. Wilson v_, Dec 22 2004
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