Before I started this Mathematics blog in the second half of 2015, I had started making some mathematical posts in my Pedagogical Posturing blog. I only remembered this when I was looking back over posts that I had made to that blog which I had begun in March of 2009. The first mathematical post I made was on August 5th of 2013 and was titled Reflections on 23500.
The main point that emerged from this post was that, while rounding off to the nearest thousand is common enough, it's also the case that rounding off to the nearest multiple of 500 is also popular, especially when the numbers involved are not large. This is why the number popped up in reference to the populations of various towns and cities, both currently and historically.
The other interesting fact about this number was that the centre of the Sun is about 23500 times more distant from us than the centre of the Earth (source). Thus:$$\text{radius of Earth }: \text{ radius of Earth's orbit }: : 1:23500$$Of course, this again is an approximation or rounding off of the more accurate figure of 23,460 earth radii or \(1.496 \times 10^{11}\) metres (termed an Astronomical Unit or AU).
Because of my reliance on the OEIS, I often look at a number in terms of its membership in various sequences but many numbers, like 23500, have a standalone physical significance. Here is the full post made almost 11 years ago now:
Today I'm 23500 days old and I was looking around to see if there was any significance to this number. It's factors are unremarkable, \(2^2 \times 5^3 \times 47 \), but the fact that it's halfway between 23000 and 24000 means that it pops up quite frequently in Internet searches, as would 22500 or 24500 I would imagine. A search reveals that the approximate population of Boston in 1620 was 23500 and there are several towns around the world that are listed as having this population currently e.g. Bishopbriggs in Scotland.
Bishopbriggs grew from a small rural village on the old road from Glasgow to Kirkintilloch and Stirling during the 19th century, eventually growing to incorporate the adjacent villages of Auchinairn, Cadder, Jellyhill and Mavis Valley. It currently has a population of approximately 23,500 people.
It turns out that Mount Isa has the same population (source):
Mount Isa is located just 200 kilometres from the Northern Territory border and 1,829 kilometres from Queensland’s capital, Brisbane. The nearest major city, Townsville, can be found 883 kilometres from The Isa. Mount Isa covers an area of over 43,310 square kilometres, making it geographically the second largest city in Australia to Kalgoorlie-Boulder, Western Australia ... With a population of approximately 23,500, Mount Isa is a major service centre for north-west Queensland.
Many other examples of towns having populations of about 23500 could be quoted. In addition of populations, the number sometimes comes up as a dollar figure (source):
In its third annual funding cycle, the Black Philanthropy Initiative has pumped $23,500 back into the Winston-Salem area to help African Americans improve their parenting skills.
Interestingly, it turns out that the centre of the Sun is about 23500 times more distant from us than the centre of the Earth (source).
The sun is far enough away (about 23,500 earth radii) that it took a long time before people knew accurately how far away the sun was. Certainly the ancient Greeks had calculated the distance, but they also knew that their results could be off.
Many countries in the world have five digit postal codes or zip codes as they are sometimes known. These codes identify particular locations within the country e.g. Muang Prachinburi, Prachinburi, Thailand has a postcode of 23500. The United States uses a five digit system but apparently there is no location corresponding to 23500, although there is for 23499 and 23501.
At the time I made this post, I hadn't discovered the OEIS although I was aware of it in late 2014 or early 2015. Nor had I discovered Numbers Aplenty and several other resources that have proved most helpful in finding out more about numbers.
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