OFFSET
0,8
COMMENTS
A015886(n) gives the position of the first zero in the n-th row of this array.
LINKS
Michel Marcus, Table of n, a(n) for n = 0..5049
FORMULA
T(0, k) = 0 for all k.
EXAMPLE
Array begins:
0, 0, 0, 0, 0, 0, 0, ...
1, 0, 2, -2, 5, -5, 6, ...
1, 2, 0, 3, 0, 1, 3, ...
3, 0, 5, -2, 6, -2, 7, ...
1, 5, 0, 4, 3, 2, 0, ...
6, 0, 6, 1, 7, -5, 15, ...
1, 6, 3, 5, 0, 10, 0, ...
7, 3, 7, -2, 15, -5, 9, ...
...
MATHEMATICA
Table[Function[n, If[k + n == 0, 0, DivisorSigma[1, k + n]] - If[k == 0, 0, DivisorSigma[1, k]] - n][m - k], {m, 12}, {k, m, 1, -1}] // Flatten (* Michael De Vlieger, Jul 20 2017 *)
PROG
(PARI) T(n, k) = sigma(k + n) - sigma(k) - n;
(PARI) a(n) = n++; my(s = ceil((-1+sqrt(1+8*n))/2)); r=n-binomial(s, 2)-1; k=s-r; T(r, k) \\ David A. Corneth, Jul 20 2017
(Python)
from sympy import divisor_sigma
l=[]
def T(n, k):
return 0 if n==0 or k==0 else divisor_sigma(k + n) - divisor_sigma(k) - n
for n in range(11): l+=[T(k, n - k + 1) for k in range(n + 1)]
print(l) # Indranil Ghosh, Jul 21 2017
CROSSREFS
KEYWORD
sign,tabl
AUTHOR
Michel Marcus, Jul 20 2017
STATUS
approved