A101306 a(n) = Sum_{i=1..n} {last digit of prime(i)}.

2, 5, 10, 17, 18, 21, 28, 37, 40, 49, 50, 57, 58, 61, 68, 71, 80, 81, 88, 89, 92, 101, 104, 113, 120, 121, 124, 131, 140, 143, 150, 151, 158, 167, 176, 177, 184, 187, 194, 197, 206, 207, 208, 211, 218, 227, 228, 231, 238, 247, 250, 259, 260, 261, 268, 271, 280

Offset

1,1

Comments

Asymptotically, a(n) ~ 5n by Dirichlet's theorem. - Charles R Greathouse IV, Sep 28 2008

Links

Table of n, a(n) for n=1..57.

Example

a(1) = 2;
a(2) = 2 + 3 = 5;
a(3) = 2 + 3 + 5 = 10;
a(4) = 2 + 3 + 5 + 7 = 17;
a(5) = 2 + 3 + 5 + 7 + 1(1) = 2 + 3 + 5 + 7 + 1 = 18.

Mathematica

f[n_] := Sum[ Mod[ Prime[i], 10], {i, n}]; Array[ f, 60] (* Robert G. Wilson v, Dec 22 2004 *)
Rest@ FoldList[Plus, 0, Mod[Prime@ Range@ 60, 10]] (* Robert G. Wilson v, Jan 16 2011 *)

Prog

(PARI) sum(k=1, n, prime(k)%10) \\ Charles R Greathouse IV, Sep 28 2008

Crossrefs

Partial sums of A007652.

Sequence in context: A264300 A326763 A067112 * A051351 A111925 A238804

Adjacent sequences: A101303 A101304 A101305 * A101307 A101308 A101309

Keyword

nonn,base,easy

Author

Jorge Coveiro, Dec 22 2004

Extensions

Corrected and extended by Robert G. Wilson v, Dec 22 2004

Status

approved