A274093 a(0)=0; thereafter (-1)^n*n appears n times.

0, -1, 2, 2, -3, -3, -3, 4, 4, 4, 4, -5, -5, -5, -5, -5, 6, 6, 6, 6, 6, 6, -7, -7, -7, -7, -7, -7, -7, 8, 8, 8, 8, 8, 8, 8, 8, -9, -9, -9, -9, -9, -9, -9, -9, -9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12

Offset

0,3

Links

Chai Wah Wu, Table of n, a(n) for n = 0..10011

Maple

s1:=[0];
for n from 1 to 15 do
   for i from 1 to n do
     s1:=[op(s1), (-1)^n*n]; od: od:
s1;

Mathematica

Join[{0}, Flatten[Table[(-1)^n*n, {n, 15}, {n}]]] (* Paolo Xausa, Sep 30 2024 *)
Join[{0}, Table[PadRight[{}, n, If[EvenQ[n], n, -n]], {n, 15}]]//Flatten (* Harvey P. Dale, Dec 06 2024 *)

Prog

(Python)
A274093_list = [0]+ [i for n in range(1, 142) for i in [-n if n % 2 else n]*n] # Chai Wah Wu, Jun 11 2016
(Python)
from math import isqrt
def A274093(n): return -m if (m:=isqrt(n<<3)+1>>1)&1 else m # Chai Wah Wu, Nov 05 2024

Crossrefs

Cf. A002024, A274094.

Sequence in context: A253272 A023965 A274094 * A087847 A107436 A002024

Adjacent sequences: A274090 A274091 A274092 * A274094 A274095 A274096

Keyword

sign

Author

N. J. A. Sloane, Jun 10 2016

Status

approved