|
Search: id:A126073
|
|
|
| A126073 |
|
Sum of numbers <= n which are multiples of 3 or 5 but not 15. |
|
+0
3
|
|
| 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; listen)
|
|
|
OFFSET
|
1,3
|
|
|
COMMENT
|
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.
|
|
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: A052407 A105039 A090597 this_sequence A126592 A055057 A154029
Adjacent sequences: A126070 A126071 A126072 this_sequence A126074 A126075 A126076
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Zak Seidov (zakseidov(AT)gmail.com), Mar 13 2007
|
|
|
Search completed in 0.002 seconds
|
