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A230477 Smallest number that is the sum of n positive n-th powers in >= n ways. 6
1, 50, 5104, 236674, 9006349824 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Does a(6) exist? For which values of n does a(n) exist? Is there a proof that a(n) < a(n+1) when both exist?

REFERENCES

A. H. Beiler, Recreations in the Theory of Numbers: The Queen of Mathematics Entertains, Dover, NY, 1966, pp. 162-165, 290-291.

R. K. Guy, Unsolved Problems in Number Theory, 3rd edition, Springer, 2004, D1.

LINKS

Table of n, a(n) for n=1..5.

Open Directory Project, Equal Sums of Like Powers

FORMULA

a(n) <= A146756(n), with equality at least for n = 1, 3, 5 and inequality at least for n = 2, 4.

a(n) >= A091414(n) for n > 1, with equality at least for n = 2 and inequality at least for n = 3, 4, 5.

EXAMPLE

1 = 1^1.

50 = 1^2 + 7^2 = 5^2 + 5^2.

5104 = 1^3 + 12^3 + 15^3 = 2^3 + 10^3 + 16^3 = 9^3 + 10^3 + 15^3.

236674 = 1^4 + 2^4 + 7^4 + 22^4 = 3^4 + 6^4 + 18^4 + 19^4 = 7^4 + 14^4 + 16^4 + 19^4 = 8^4 + 16^4 + 17^4 + 17^4.

9006349824 = 8^5 + 34^5 + 62^5 + 68^5 + 92^5 = 8^5 + 41^5 + 47^5 + 79^5 + 89^5 = 12^5 + 18^5 + 72^5 + 78^5 + 84^5 = 21^5 + 34^5 + 43^5 + 74^5 + 92^5 = 24^5 + 42^5 + 48^5 + 54^5 + 96^5.

CROSSREFS

a(2) = A048610(2), a(3) = A025398(1), a(4) = A219921(1).

Cf. A146756 (smallest number that is the sum of n distinct positive n-th powers in exactly n ways), A230561 (smallest number that is the sum of two positive n-th powers in >= n ways), A091414 (smallest number that is the sum of n positive n-th powers in >= 2 ways).

Sequence in context: A248205 A174756 A231937 * A320099 A115436 A184555

Adjacent sequences:  A230474 A230475 A230476 * A230478 A230479 A230480

KEYWORD

nonn,more,hard

AUTHOR

Jonathan Sondow, Oct 22 2013

EXTENSIONS

a(5) from Donovan Johnson, Oct 23 2013

STATUS

approved

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Last modified May 31 00:53 EDT 2020. Contains 334747 sequences. (Running on oeis4.)