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a(n) = n^2 XOR triangular(n), where XOR is the bitwise logical exclusive-or operator.
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%I #13 Jun 10 2020 17:41:26

%S 0,0,7,15,26,22,49,45,100,124,83,59,222,242,173,153,392,440,495,471,

%T 322,350,281,773,876,820,1019,931,646,762,597,561,1552,1648,1751,1727,

%U 1930,2022,1857,1789,1396,1484,1379,1163,1102,994,3197,3273,3480,3496,3391,3847,4082

%N a(n) = n^2 XOR triangular(n), where XOR is the bitwise logical exclusive-or operator.

%F a(n) = A000290(n) XOR A000217(n).

%e a(2) = 2^2 xor 2*3/2 = 4 xor 3 = 7.

%t Table[BitXor[n^2,(n(n+1))/2],{n,0,60}] (* _Harvey P. Dale_, Aug 11 2017 *)

%o (Python)

%o for n in range(99):

%o print((n*n) ^ (n*(n+1)//2), end=", ")

%Y Cf. A000290, A000217.

%K nonn,base

%O 0,3

%A _Alex Ratushnyak_, Jun 08 2013