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 A206825 Number of solutions (n,k) of k^4=n^4 (mod n), where 1<=k
 0, 0, 1, 0, 0, 0, 3, 2, 0, 0, 1, 0, 0, 0, 7, 0, 2, 0, 1, 0, 0, 0, 3, 4, 0, 8, 1, 0, 0, 0, 7, 0, 0, 0, 5, 0, 0, 0, 3, 0, 0, 0, 1, 2, 0, 0, 7, 6, 4, 0, 1, 0, 8, 0, 3, 0, 0, 0, 1, 0, 0, 2, 15, 0, 0, 0, 1, 0, 0, 0, 11, 0, 0, 4, 1, 0, 0, 0, 7, 26, 0, 0, 1, 0, 0, 0, 3, 0, 2, 0, 1, 0, 0, 0, 7, 0, 6, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,7 LINKS Antti Karttunen, Table of n, a(n) for n = 2..16384 EXAMPLE 8 divides exactly three of the numbers 8^4-k^4 for k = 1, 2 , ..., 7, so that a(8) = 3. MATHEMATICA s[k_] := k^4; f[n_, k_] := If[Mod[s[n] - s[k], n] == 0, 1, 0]; t[n_] := Flatten[Table[f[n, k], {k, 1, n - 1}]] a[n_] := Count[Flatten[t[n]], 1] Table[a[n], {n, 2, 120}]  (* A206825 *) PROG (PARI) A206825(n) = { my(n4 = n^4); sum(k=1, n-1, !((n4-(k^4))%n)); }; \\ Antti Karttunen, Nov 17 2017 CROSSREFS Cf. A206590. Sequence in context: A324881 A305930 A206590 * A336551 A292380 A242165 Adjacent sequences:  A206822 A206823 A206824 * A206826 A206827 A206828 KEYWORD nonn AUTHOR Clark Kimberling, Feb 12 2012 STATUS approved

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Last modified December 1 14:10 EST 2021. Contains 349430 sequences. (Running on oeis4.)