A081406 a(n) = (n+1)*a(n-3), a(0)=a(1)=a(2)=1 for n>1.

1, 1, 1, 4, 5, 6, 28, 40, 54, 280, 440, 648, 3640, 6160, 9720, 58240, 104720, 174960, 1106560, 2094400, 3674160, 24344320, 48171200, 88179840, 608608000, 1252451200, 2380855680, 17041024000, 36321084800, 71425670400, 528271744000, 1162274713600

Offset: 0

Author

Labos Elemer, Apr 01 2003

Keywords

• nonn

Examples

			a(3n+2)=A034001[n]; while other subsequences are near(but not equal) to A001669, A000359.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A002866, A000142, A001147, A081405.

Programs

GAP

a:= function(k)
    if k<3 then return 1;
    elif k<6 then return k+1;
    else return (k+1)*a(k-3);
    fi;
  end;
List([0..35], n-> a(n) ); # G. C. Greubel, Aug 24 2019

Magma

a:= func< n | n le 2 select 1 else n in [3..5] select n+1 else (n+1)*Self(n-2) >;
[a(n): n in [0..35]]; // G. C. Greubel, Aug 24 2019

Mathematica

f[n_]:= (n+1)*f[n-3]; f[0]=1; f[1]=1; f[2]=1; Table[f[n], {n, 30}]
RecurrenceTable[{a[0]==a[1]==a[2]==1,a[n]==(n+1)a[n-3]},a,{n,30}] (* Harvey P. Dale, Mar 06 2019 *)

PARI

a(n) = if(n<3, 1, (n+1)*a(n-3) );
vector(35, n, a(n-1)) \\ G. C. Greubel, Aug 24 2019

Sage

def a(n):
    if n<3: return 1
    elif 3<= n <= 5: return n+1
    else: return (n+1)*a(n-3)
[a(n) for n in (0..35)] # G. C. Greubel, Aug 24 2019

Extensions

Corrected and extended by Harvey P. Dale, Mar 06 2019