 Above, a 1934 plaque from the Big Apple Night Club at West 135th Street and Seventh Avenue in Harlem. Discarded as trash in 2006.

Entry from February 08, 2016
“Why do mathematicians like parks?"/"Because of all the natural logs.”

A popular math joke is:

Q: Why do mathematicians like parks?
A: Because of all the natural logs.

The natural logarithm ("natural logs") joke has been cited in print since at least 2006. “Q: Why do mathematicians like forests? A: Natural logs!” was cited on Twitter on March 2, 2009.

Wikipedia: Natural logarithm
The natural logarithm of a number is its logarithm to the base of the mathematical constant e, where e is an irrational and transcendental approximately equal to 2.718281828459. The natural logarithm of x is generally written as ln x, loge x, or sometimes, if the base e is implicit, simply log x. Parentheses are sometimes added for clarity, giving ln(x), loge(x) or log(x). This is done in particular when the argument to the logarithm is not a single symbol, to prevent ambiguity.

Wikipedia: Mathematical joke (6 October 2006 page revision)
A mathematical joke is a form of professional humor which relies on aspects of mathematics or a stereotype of mathematicians to derive humor. The humor may come from a pun or double meaning of a mathematical term, or on a non-mathematician’s misunderstanding of a mathematical concept. Such jokes are frequently inaccessible to those without a mathematical bent.

Pun-based jokes
Why do Mathematicians like national parks?
Because of the natural logs.

mafiascum
Alduskkel
Thu Feb 12, 2009 6:45 am
Why do mathematicians like parks? For all the natural logs!

Hilary Mason
‏@hmason
I am WAY too amused by the Wikipedia ‘mathematical joke’ page: http://bit.ly/2PI3 Q: Why do mathematicians like forests? A: Natural logs!
9:03 AM - 2 Mar 2009

Studentawards Forum
Physics, math, engineering & comsci jokes
Superman6424
Posted: January 25, 2010 4:39:30 PM
(...)
Why do mathematicians like parks?
Because of the natural logs.

Ms. Barbara Woodcock
‏@mswoodcockmath
Why do mathematicians like forests? Because they’re full of natural logs! #MathJokeMonday
6:47 AM - 4 Nov 2013

Jake Thiessen
‏@TotesJake
@JessicaNaslund
Why do mathematicians like parks?
Because of all the natural logs
9:59 PM - 30 Apr 2014

Holiday Inn Express
‏@hiegeorgetown
Have you ever wondered why mathematicians like parks?  I found out it was because of all the natural logs. #mathjokes
7:15 PM - 1 May 2014

3D home tutorsㅿ
April 18, 2015 ·
Q: Why do mathematicians like parks?
A: Because of all the natural logs.

Yaar Kahin Aap Love Guru Toh Nahi
May 22, 2015 ·
Q: Why do mathematicians like parks?
A: Because of all the natural logs