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

1,1

Comments

The differences are always odd since the parity of A101306 and n are always opposite.

Positions where a(n)=2k-1 for k>0; 10, 1, 2, 5, 6, 20, 21, 62, 64, 65, 67, 198, 761, 765, 764, 800, ... - Robert G. Wilson v, Jun 06 2012

Links

Table of n, a(n) for n=1..80.

Formula

a(n) = 5*n - Sum_{i=1..n} Prime(i) (mod 10).

Mathematica

f[n_] := 5n - Sum[ Mod[ Prime@ k, 10], {k, n}]; Array[f, 80]
Rest@ FoldList[# + 5 - Mod[Prime@ #2, 10] &, 0, Range@ 80]

Crossrefs

Cf. A101306, A122754, A184594.

Sequence in context: A053670 A085963 A282177 * A328154 A249304 A333906

Adjacent sequences: A184590 A184591 A184592 * A184594 A184595 A184596

Keyword

base,easy,sign

Author

Robert G. Wilson v, Jan 17 2011

Status

approved