OFFSET
0,3
COMMENTS
Sum of reciprocals = 2.2472460058071954531775930749...
MAPLE
a:= proc(n) option remember;
`if`(n=0, 1, 2*((n-1)*a(n-1)+n)-1)
end:
seq(a(n), n=0..20); # Alois P. Heinz, Mar 14 2023
MATHEMATICA
nxt[{n_, a_}]:={n+1, a*2n+2n+1}; Transpose[NestList[nxt, {1, 1}, 20]][[2]] (* Harvey P. Dale, Aug 06 2016 *)
PROG
(PARI) sum2x(n) = { s=1; sr=0; forstep(x=2, n, 2, s=x*(s+1)+1; print1(s", "); sr += 1.0/s; ); print(); print(sr) }
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Cino Hilliard, Aug 19 2003
EXTENSIONS
a(0)=1 prepended and edited by Alois P. Heinz, Mar 14 2023
STATUS
approved