perplexus.info :: Numbers : Believe it or not 2

Believe it or not 2 (Posted on 2021-12-30)

There are only 4 positive integers N such that
multiplying sod(N) by inverted(sod(N)) equals N.
The trivial number 1 qualifies !
The magic Ramanujan number 1729 qualifies as well ,
Since 19*91=1729

Now, find the missing two and prove that no other exist.

Submitted by Ady TZIDON

Rating: 4.0000 (2 votes)

Solution: (Hide)

A110921 in OEIS
1,81,1458,1729

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
D2 approach (spoiler)	Steve Herman	2021-12-31 07:24:02
computer solution	Charlie	2021-12-30 09:08:52

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