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单词 EveryEvenIntegerGreaterThan70IsTheSumOfTwoAbundantNumbersInMoreThanOneWay
释义

every even integer greater than 70 is the sum of two abundant numbers in more than one way


Theorem Every even n>70 can be expressed as n=a+b, with both a and b abundant numbers, in more than one way. Due to the commutative property of additionPlanetmathPlanetmath, swaps of a and b are not counted as separate ways.

Proof.

To prove this it is enough to find just two ways for each even n>70, though of course there are plenty more ways as the numbers get larger, purely for our convenience we’ll seek to choose the smallest values for b possible. Since every multipleMathworldPlanetmath of a perfect number is an abundant number, and 6 is a perfect number, it follows that every multiple of 6 is abundant, and it is small enough a modulusMathworldPlanetmathPlanetmath that reviewing all possible cases should not prove tiresome.

If n=6m and m>5, the two desired pairs are a=6(m-2), b=12, and a=6(m-3), b=18. This leaves us the cases n=6m+2 and n=6m+4 to concern ourselves with.

If n2mod6 and m>10 then the pairs are are a=6(m-3), b=20, and a=6(m-9), b=56.

If n4mod6 and m>12 then the pairs are a=6(m-6), b=40, and a=6(m-11), b=70.

The lower bounds of m have been chosen to ensure the formulasMathworldPlanetmathPlanetmath give distinct pairs of abundant numbers and never the perfect number 6 itself, but its multiples. These values of m correspond to the values of n 36, 68, 82. To completePlanetmathPlanetmathPlanetmathPlanetmathPlanetmathPlanetmath the proof we are left with the special case of n=76 to examine on its own. Ignoring the bounds for m, the formulas above give us 76 = 40 + 36, a valid pair, and 76 = 70 + 6, which is not a pair of abundant numbers. But there is one other pair, 56 + 20, of which neither a nor b is a multiple of 6.∎

The special case of 76 shows that there are solutions that don’t use multiples of 6. These become more readily available as the numbers get larger.

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更新时间:2025/5/4 18:36:34