This app was mentioned in 15 comments, with an average of 2.07 upvotes
My top calculator is actually this one, but the free version is forcibly ad-powered and I think the pro version only ever went on a giveaway once, to my memory: https://play.google.com/store/apps/details?id=us.mathlab.android.calc.edu
If I didn't have this then I'd totally use Mobi!
I second Graphing Calculator + Math PRO as the only paid calculator app everyone needs, even if you never use the graphing portion of it. The reason is that it is the only calculator (that I've found, anyways) that:
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everUp until I tried Mathlab's calc, the calculator that used to reign king for that was Mobi Calculator, but Bluetooth keyboard input would double numbers (so if you typed "3," it would put "33" and also Backspace that many times, inconsistently depending on what other characters you may have entered or arrow key movement done).
If you don't ever use Bluetooth keyboard input nor advanced graphing features, I would recommend MobiCalc because the buttons are bigger and easier to press and are slightly more customizable.
I got a graphing calculator free on sale a while back and it seems decent. There's a free version as well, with 5m downloads.
https://play.google.com/store/apps/details?id=us.mathlab.android.calc.edu
The one I use is this one, it doesn't look fancy but is damn smooth to use even on a mobile UI, which was surprising to me.
Buat mahasiswa jurusan STEM dan pakai Android, coba cek Graphing Calculator + Math buatannya Mathlab. Menurut gua itu calculator yang bener2 nyaris bisa apa aja. Dia bisa nyelesaiin persamaan linear, operasi matriks, kalkulus (integral, turunan), penggambaran banyak grafik di satu window yang sama (koordinat polar / kartesian), grafik 3D, bisa basic statistic (mean, stddev, dll.) juga, dll. Really cheap alternative for a real graphing calculator. Sangat berguna buat matkul fundamental seperti Kalkulus atau Aljabar Linear. Selain buat belajar, gua juga pake ini buat ngajarin matkul kayak Kalkulus ama Aljabar Linear ke adek tingkat sebagai visualisasi atau pembuktian hasil perhitungan. Ada versi free juga sih, tp gua recommend yang pro karena ga mahal-mahal amat sebenernya
$9 US, Google Play link
Graphing Calculator by Mathlab is great but it costs ~5€.
MathStudio Express should do pretty much everything you'd ever want but costs 25€.
There is also WolframAlpha but it requires an internet connection to use and costs ~3€. I'm not sure if that has changed but earlier versions of the app gave you step-by-step solutions for free, while being a paid feature to use on the main website.
If you don't like either of those, an emulator for a Texas Instruments calculator might be for you. However, it requires work to set up. I can recommend these ones:
Andie Graph (free)
Graph 89 (~3€)
AlmostTI (5€)
How does it stack up to Mathlab, though? https://play.google.com/store/apps/details?id=us.mathlab.android.calc.edu
MathLabs best calculator graphing app I've used. Surprised it isn't mentioned.
https://play.google.com/store/apps/details?id=us.mathlab.android.calc.edu
It's a one time $10 USD purchase, but it's like a top tier TI graphing calc.
If you need an actual calculator:
https://play.google.com/store/apps/details?id=us.mathlab.android.calc.edu
https://play.google.com/store/apps/details?id=cz.hipercalc
https://play.google.com/store/apps/details?id=com.realmax.calc
https://play.google.com/store/apps/details?id=com.mathally.calculator.pro
These are Casio-style ones, if you prefer Texas Instruments, there's AlmostTI (haven't tried that one), Graph89, and Wabbitemu.
I don't know what you need from a calc app, but this has done everything I need in engineering:
https://play.google.com/store/apps/details?id=us.mathlab.android.calc.edu