OFFSET
1,2
COMMENTS
These are the sums arising in A054464.
LINKS
Robert Israel, Table of n, a(n) for n = 1..1793
FORMULA
From Robert Israel, Aug 07 2016: (Start)
For d >=2, the m with d digits are the solutions of x^2 + x - 9*10^(d-1)*d - 10^(d-1) == 0 (mod 2*10^d) with 10^(d-1) <= x < 10^d.
The corresponding a(n) are m(m+1)10^(-d)/2 + (10^d-9d-1)/20. (End)
MAPLE
T:= (x, d) -> ((1/2)*x^2+(1/2)*x)*10^(-d)-(9/20)*d+(1/20)*10^d-1/20:
F:= proc(d) local x, S;
S:= map(t -> subs(t, x), [msolve(x^2 + x - 9*10^(d-1)*d - 10^(d-1), 2*10^d)]);
op(map(T, sort(select(t -> t >= 10^(d-1) and t < 10^d, S)), d))
end proc:
[1, op(map(F, [$2..30]))]; # Robert Israel, Aug 07 2016
CROSSREFS
KEYWORD
nonn,base
AUTHOR
N. J. A. Sloane, Aug 07 2016
STATUS
approved