A284630 a(1)=1, a(2)=2; for n > 1, a(n+1) = (a(n-1) mod n) + n.

1, 2, 3, 5, 7, 5, 7, 12, 15, 12, 15, 12, 15, 25, 15, 25, 31, 25, 31, 25, 31, 25, 31, 25, 31, 25, 31, 52, 31, 52, 31, 52, 63, 52, 63, 52, 63, 52, 63, 52, 63, 52, 63, 52, 63, 52, 63, 52, 63, 52, 63, 52, 63, 105, 63, 105, 63, 105, 63, 105, 63, 105, 63, 105, 127, 105, 127, 105, 127, 105, 127, 105, 127, 105, 127, 105, 127, 105, 127, 105

Offset: 1

Author

Thomas Kerscher, Mar 31 2017

Keywords

• nonn
• easy
• look

Examples

			a(3) = a(1) (mod 2) + 2 = 3.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A003817.

Programs

Maple

A[1]:= 1: A[2]:= 2:
for n from 3 to 200 do A[n]:= (A[n-2] mod (n-1)) + n-1 od:
seq(A[n],n=1..200); # Robert Israel, Apr 04 2017

Mathematica

a[n_] := a[n] = If[n < 3, n, Mod[a[n - 2], n - 1] + n - 1]; Array[a, 80] (* Michael De Vlieger, Apr 02 2017 *)
nxt[{n_,a_,b_}]:={n+1,b,Mod[a,n]+n}; NestList[nxt,{2,1,2},100][[;;,2]] (* Harvey P. Dale, Jul 31 2023 *)

PARI

a(n) = if (n<=2, n, (n-1) + a(n-2) % (n-1)); \\ Michel Marcus, Apr 02 2017