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A126073 Sum of numbers <= n which are multiples of 3 or 5 but not 15. 2
0, 0, 3, 3, 8, 14, 14, 14, 23, 33, 33, 45, 45, 45, 45, 45, 45, 63, 63, 83, 104, 104, 104, 128, 153, 153, 180, 180, 180, 180, 180, 180, 213, 213, 248, 284, 284, 284, 323, 363, 363, 405, 405, 405, 405, 405, 405, 453, 453, 503, 554, 554, 554, 608, 663, 663, 720, 720 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Sum of numbers m<=n such that mod(m,3)*mod(m,5)=0 and mod(m,15)>0.

First differences (fd) are

0,3,0,5,6,0,0,9,10,0,12,0,0,0,0,

0,18,0,20,21,0,0,24,25,0,27,0,0,0,0,

0,33,0,35,36,0,0,39,40,0,42,0,0,0,0,...

fd(1..15)={0,3,0,5,6,0,0,9,10,0,12,0,0,0,0}; for n>15

fd(n)=fd(n-15)+15 if fd(n-15)>0, fd(n)=0 otherwise.

LINKS

Table of n, a(n) for n=1..58.

FORMULA

an[n,d]=d*Floor[n/d];sn[n,d]=(an[n,d]*(an[n,d] + d))/(2*d); a(n)=sn[n,3]+sn[n,5]-2*sn[n,15].

MATHEMATICA

an[n_, d_]:=d*Floor[n/d]; sn[n_, d_]:=(an[n, d]*(an[n, d] + d))/(2*d); Table[sn[n, 3]+sn[n, 5]-2*sn[n, 15], {n, 1000}]

CROSSREFS

Cf. A126590, A126592.

Sequence in context: A303902 A090597 A304887 * A126592 A055057 A154029

Adjacent sequences:  A126070 A126071 A126072 * A126074 A126075 A126076

KEYWORD

nonn

AUTHOR

Zak Seidov, Mar 13 2007

STATUS

approved

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Last modified September 22 20:30 EDT 2018. Contains 315270 sequences. (Running on oeis4.)