Sagan's number

Sagan's number, named after Carl Sagan, is the number of stars in the observable universe, currently estimated to be 70 sextillion or \(7 \times 10^{22}\).
A related term, the sagan, is defined as four billion.http://www.neatorama.com/2009/11/09/10-neat-facts-about-carl-sagan
== Approximations ==
Notation 	Lower bound 	Upper bound
Scientific notation 	\(7\times10^{22}\) 	\(7\times10^{22}\)
Arrow notation 	\(80\uparrow12\) 	\(43\uparrow14\)
Steinhaus-Moser Notation 	18[3] 	19[3]
Copy notation 	6[23] 	7[23]
Taro's multivariable Ackermann function	A(3,72) 	A(3,73)
Pound-Star Notation 	#*(0,1,3,2)*5 	#*(4,1,6,10)*4
BEAF 	{80,12} 	{43,14}
Hyper-E notation 	7E22 	7E22
Bashicu matrix system 	(0)(0)(0)[717] 	(0)(0)(0)[718]
Hyperfactorial array notation 	23! 	24!
Fast-growing hierarchy 	\(f_2(69)\) 	\(f_2(70)\)
Hardy hierarchy 	\(H_{\omega^2}(69)\) 	\(H_{\omega^2}(70)\)
Slow-growing hierarchy 	\(g_{\omega^{\omega2+2}7}(10)\)	\(g_{\omega^{\omega2+2}7}(10)\)
== Sources ==
== See also ==
Category:Numbers
Category:Class 2
Category:Eponymous numbers
Category:Non-powers
Category:Numbers with 7 to 29 digits