OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
R. Donaghey, Binomial self-inverse sequences and tangent coefficients, J. Combin. Theory, Series A, 21 (1976), 155-163.
FORMULA
a(n) = 2 * A005425(n-1), n > 0.
a(n) ~ sqrt(2)*exp(2*sqrt(n)-n/2-1)*n^(n/2-1/2). - Vaclav Kotesovec, Oct 08 2012
MATHEMATICA
RecurrenceTable[{a[0]==1, a[1]==2, a[n]==2 a[n-1] + (n-2) a[n-2]}, a, { n, 40}] (* Vincenzo Librandi, Dec 29 2012 *)
Table[If[n==0, 1, 2*(-I/Sqrt[2])^(n-1)*HermiteH[n-1, I*Sqrt[2]]], {n, 0, 40}] (* G. C. Greubel, Apr 01 2023 *)
PROG
(Magma) [n le 2 select n else 2*Self(n-1) + (n-3)*Self(n-2): n in [1..40]]; // G. C. Greubel, Apr 01 2023
(SageMath) [1]+[2*(-i/sqrt(2))^(n-1)*hermite(n-1, i*sqrt(2)) for n in range(1, 41)] # G. C. Greubel, Apr 01 2023
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved