OFFSET
1,1
COMMENTS
Equivalently, numbers k such that (k + 10)*10 is a square.
The positive terms belong to the fourth column of the array in A185781.
LINKS
Bruno Berselli, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
O.g.f.: -10*x*(1 - 3*x)/(1 - x)^3.
E.g.f.: -10*x*(1 - x)*exp(x).
a(n) = a(2-n).
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3).
a(n) = 10*n*(n - 2) = 10*A067998(n).
a(n) = A033583(n-1) - 10. - Altug Alkan, Apr 10 2018
MATHEMATICA
Table[10 n (n - 2), {n, 1, 50}]
PROG
(PARI) vector(50, n, nn; 10*n*(n-2))
(Maxima) makelist(10*n*(n-2), n, 1, 50);
(GAP) List([1..50], n -> 10*n*(n-2));
(Julia) [10*n*(n-2) for n in 1:50] |> println
(Sage) [10*n*(n-2) for n in (1..50)]
(Python) [10*n*(n-2) for n in range(1, 50)]
(Magma) [10*n*(n-2): n in [1..50]];
CROSSREFS
After -10, subsequence of A174133 because a(n) = ((n-1)^2-1)*(3^2+1).
KEYWORD
sign,easy
AUTHOR
Bruno Berselli, Apr 10 2018
STATUS
approved