A064568 - OEIS

%I #39 Sep 28 2024 01:45:26

%S 1,3,11,21,39,76,248,844,1520,2752,9317,17223,31221,57071,99741,

%T 589932,58056875,101769229,302890748,511561220,904036924,39488697700,

%U 325374626148,535755688021,1404720439053,3883018238329,6283167591179,16166305650060,25735985498861,40806937801472

%N n-th term in Recamán's sequence A005132 is divisible by n.

%C No more terms < 4.61*10^11. - _Jud McCranie_, Dec 29 2019

%C No more terms < 6.46*10^13. - _James Ewens_, Sep 27 2024

%H <a href="/index/Rea#Recaman">Index entries for sequences related to Recamán's sequence</a>

%e A005132(21) = 63, 63 is divisible by 21, so 21 is in the sequence.

%t With[{s = Nest[Append[#1, If[And[#3 > 0, FreeQ[#1, #3]], #3, #1[[-1]] + #2]] & @@ {#1, #2, #1[[-1]] - #2} & @@ {#, Length@ #} &, {0}, 10^5]}, Reap[Do[If[Mod[s[[i]], i] == 0, Sow[i]], {i, Length@ s - 1}]][[-1, -1]]] (* _Michael De Vlieger_, Dec 29 2019 *)

%Y Cf. A005132, A064569.

%K nonn,more

%O 1,2

%A _N. J. A. Sloane_, Oct 16 2001

%E Offset changed, a(1), a(22)-a(23) from _Jud McCranie_, Dec 29 2019

%E a(24)-a(30) from _James Ewens_, Sep 27 2024