Fourth Powers which are Sum of 4 Fourth Powers/Examples/353
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Examples of Fourth Powers which are Sum of 4 Fourth Powers
- $353^4 = 30^4 + 120^4 + 272^4 + 315^4$
Proof
\(\ds 30^4 + 120^4 + 272^4 + 315^4\) | \(=\) | \(\ds 810 \, 000\) | ||||||||||||
\(\ds \) | \(\) | \(\, \ds + \, \) | \(\ds 207 \, 360 \, 000\) | |||||||||||
\(\ds \) | \(\) | \(\, \ds + \, \) | \(\ds 5 \, 473 \, 632 \, 256\) | |||||||||||
\(\ds \) | \(\) | \(\, \ds + \, \) | \(\ds 9 \, 845 \, 600 \, 625\) | |||||||||||
\(\ds \) | \(=\) | \(\ds 15 \, 527 \, 402 \, 881\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 353^4\) |
Now we have that:
\(\ds 442^2 - 272^2\) | \(=\) | \(\ds 170 \times 714\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 17^2 \times 420\) |
Hence:
\(\ds 442^2 - 3 \times 17^2\) | \(=\) | \(\ds 272^2 + 289 \times 417\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 272^2 + 353^2 - 64^2\) |
But:
- $3 \times 17 = 2 \times 26 - 1$
So:
\(\ds 442^2 - 2 \times 26 \times 17 + 17\) | \(=\) | \(\ds 442^2 - 2 \times 442 + 17\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 441^2 + 4^2\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 21^4 + 2^4\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 272^2 + 353^2 - 8^4\) |
Hence:
- $353^2 + 272^2 = 2^4 + 8^4 + 21^4$
but:
\(\ds 353^2 - 272^2\) | \(=\) | \(\ds 81 \times 625\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 15^4\) |
So:
- $353^4 = 30^4 + 120^4 + 272^4 + 315^4$
$\blacksquare$
Historical Note
This result was discovered by Robert Norrie, who reported on it in $1911$.
Sources
- 1911: Robert Norrie: On the Algebraic Solutions of Indeterminate Cubic and Quartic Equations (University of Saint Andrews Five Hundredth Anniversary Memorial Volume pp. 47 – 92) (edited by William Carmichael McIntosh, John Edward Aloysius Steggall and James Colquhoun Irvine)
- Nov. 1964: Kenneth S. Williams: On Norrie's Identity (Math. Mag. Vol. 37, no. 5: p. 322) www.jstor.org/stable/2689242
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $353$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $353$
- Piezas, Tito III and Weisstein, Eric W. "Diophantine Equation--4th Powers." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DiophantineEquation4thPowers.html