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A210256 Differences of the sum of distinct values of {floor(n/k), k=1,...,n}. 1
2, 1, 3, 1, 4, 1, 2, 4, 2, 1, 6, 1, 2, 2, 6, 1, 3, 1, 7, 2, 2, 1, 4, 6, 2, 2, 3, 1, 9, 1, 3, 2, 2, 2, 10, 1, 2, 2, 4, 1, 10, 1, 3, 3, 2, 1, 5, 8, 3, 2, 3, 1, 4, 2, 11, 2, 2, 1, 6, 1, 2, 3, 11, 2, 4, 1, 3, 2, 4, 1, 14, 1, 2, 3, 3, 2, 4, 1, 5, 11, 2, 1, 6, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Differences of A051201.

It appears that a(n)=1 if and only if n>1 and n+1 is a prime.  For example, the indices where 1 occurs in {a(n)} are {2,4,6,10,12,16,...}.  Adding 1 to each of these gives {3,5,7,11,13,17,...} each of which is a prime.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..1000

MAPLE

b:= proc(n) option remember; add(i, i={seq(floor(n/k), k=1..n)}) end:

a:= n-> b(n+1)-b(n):

seq(a(n), n=1..150); # Alois P. Heinz, Mar 19 2012

CROSSREFS

Cf. A006218, A051201, A055086.

Sequence in context: A286469 A064839 A255810 * A332422 A229944 A218533

Adjacent sequences:  A210253 A210254 A210255 * A210257 A210258 A210259

KEYWORD

nonn

AUTHOR

John W. Layman, Mar 19 2012

STATUS

approved

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Last modified February 28 23:08 EST 2020. Contains 332351 sequences. (Running on oeis4.)