A184593 5n - A101306: sum_{i=1..n} the last digit of prime(i).
3, 5, 5, 3, 7, 9, 7, 3, 5, 1, 5, 3, 7, 9, 7, 9, 5, 9, 7, 11, 13, 9, 11, 7, 5, 9, 11, 9, 5, 7, 5, 9, 7, 3, -1, 3, 1, 3, 1, 3, -1, 3, 7, 9, 7, 3, 7, 9, 7, 3, 5, 1, 5, 9, 7, 9, 5, 9, 7, 11, 13, 15, 13, 17, 19, 17, 21, 19, 17, 13, 15, 11, 9, 11, 7, 9, 5, 3, 7, 3
Offset: 1
Programs
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Mathematica
f[n_] := 5n - Sum[ Mod[ Prime@ k, 10], {k, n}]; Array[f, 80] Rest@ FoldList[# + 5 - Mod[Prime@ #2, 10] &, 0, Range@ 80]
Formula
a(n) = 5*n - Sum_{i=1..n} Prime(i) (mod 10).
Comments