OFFSET
1,2
COMMENTS
a(n) <> 7 iff n equals the sum of 3 integer squares.
a(A004215(k)) = 7 for k>0;
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Square Numbers.
EXAMPLE
From Michael De Vlieger, May 08 2017: (Start)
a(4) = 1 since 4 = 1 * 4^1 and 4 / 4^1 = 1; 1 = 1 (mod 8).
a(5) = 5 since it is not a multiple of 4; 5 = 5 (mod 8).
a(12) = 3 since 12 = 3 * 4^1 and 12 / 4^1 = 3; 3 = 3 (mod 8).
a(44) = 3 since 44 = 11 * 4^1 and 44 / 4^1 = 11; 3 = 11 (mod 8).
a(64) = 1 since 64 = 1 * 4^3 and 64 / 4^3 = 1; 1 = 1 (mod 8).
(End)
MATHEMATICA
Array[Mod[If[Mod[#, 4] == 0, #/4^IntegerExponent[#, 4], #], 8] &, 96] (* Michael De Vlieger, May 08 2017 *)
PROG
(Python)
def A072400(n): return (n>>((~n&n-1).bit_length()&-2))&7 # Chai Wah Wu, Aug 01 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jun 16 2002
EXTENSIONS
Offset corrected (from 0 to 1) by Antti Karttunen, May 08 2017
STATUS
approved