|
|
A159465
|
|
Sums of odd numbers, omitting squares.
|
|
1
|
|
|
3, 8, 15, 26, 39, 54, 71, 90, 111, 134, 161, 190, 221, 254, 289, 326, 365, 406, 449, 494, 541, 592, 645, 700, 757, 816, 877, 940, 1005, 1072, 1141, 1212, 1285, 1360, 1437, 1516, 1599, 1684, 1771, 1860, 1951, 2044, 2139, 2236, 2335, 2436, 2539, 2644, 2751
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
|
|
LINKS
|
|
|
FORMULA
|
a(n) = (n+S)^2 - (4*S^3-S)/3 where S = ceiling(round(sqrt(2*n-1))/2).
|
|
EXAMPLE
|
a(5) = 3 + 5 + 7 + 11 + 13 = 39.
|
|
MATHEMATICA
|
|
|
PROG
|
(Magma) S:=[ n: n in [1..108 by 2] | IsEven(SumOfDivisors(n)-2*n) ]; [ n eq 1 select S[1] else Self(n-1)+S[n]: n in [1..#S] ]; // Klaus Brockhaus, Apr 15 2009
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|