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 A088867 Nonsquarefree elements of A003824, i.e., primitive solutions to a^4 + b^4 = c^4 + d^4 with nonsquarefree value on both sides of the equation. 2
 680914892583617, 55683917506335026, 2056314197022256097, 3267700501872475297, 4544031582110882417, 10555434261160919777, 12361929340136667457, 23076050051029379057, 335875812638910622082 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Original definition was: Numbers that can be expressed as the sum of two distinct 4th powers in exactly two distinct ways that have at least one repeated factor. Among the first 516 terms of A003824, there are 31 nonsquarefree terms. None of these are expressible in more than 2 ways as sum of two 4th powers. However, some of them, as 4544031582110882417, 12361929340136667457, 335875812638910622082, ..., have gcd(a,b) > 1, for one of the decompositions a^4 + b^4. - M. F. Hasler, Mar 05 2012 LINKS D. J. Bernstein, List of 516 primitive solutions p^4 + q^4 = r^4 + s^4 FORMULA omega(n)<>bigomega(n) for n = a^4+b^4 = c^4+d^4 for distinct a, b, c, d. n=635318657, 3262811042, ..., 680914892583617, ..., 962608047985759418078417, ... EXAMPLE a(1) = A003824(18) = 680914892583617 = 17^2*89*61657*429361 is the first nonsquarefree term of A003824. - M. F. Hasler, Mar 05 2012 PROG (PARI) \ begin a new session and type \r x4data.txt (evaluated Bernstein data) This will allow using %1 as the initial value. omegax4py42(n) = { for (i = 1, n, x = eval( Str("%", i) ); y=omega(x); y1 =bigomega(x); if(y<>y1, print1(x", ")) ) } (PARI) select(A003824, t->!issquarefree(t))  \\ M. F. Hasler, Mar 05 2012 CROSSREFS Cf. A003824, A088848, A088849. Sequence in context: A297450 A172585 A321709 * A256234 A298821 A159042 Adjacent sequences:  A088864 A088865 A088866 * A088868 A088869 A088870 KEYWORD nonn AUTHOR Cino Hilliard, Nov 26 2003 STATUS approved

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Last modified December 12 01:57 EST 2019. Contains 329948 sequences. (Running on oeis4.)