Why is octave package not showing up in apt search?

I'm using 'termux'(android terminal emulator ). I've recently installed Ubuntu inside it in a 'proot' environment. When I searched for octave package using 'apt search octave' , I can't find any result. Then I manually searched for octave in Ubuntu packages to verify whether it is available for 'armhf'. To my surprise it is available for 'armhf' . I'm really dying to use octave on my android . Why is it not showing up in apt search ? What can I do to fix it?  Ubuntu package search:https://packages.ubuntu.com/search?suite=artful&arch=armhf&searchon=names&keywords=Octave Output of "cat /etc/apt/sources.list" # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to # newer versions of the distribution. deb http://ports.ubuntu.com/ubuntu-ports/ artful main restricted # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful main restricted ## Major bug fix updates produced after the final release of the ## distribution. deb http://ports.ubuntu.com/ubuntu-ports/ artful-updates main restricted # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful-updates main restricted ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu ## team. Also, please note that software in universe WILL NOT receive any ## review or updates from the Ubuntu security team. deb http://ports.ubuntu.com/ubuntu-ports/ artful universe # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful universe deb http://ports.ubuntu.com/ubuntu-ports/ artful-updates universe # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful-updates universe ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu ## team, and may not be under a free licence. Please satisfy yourself as to ## your rights to use the software. Also, please note that software in ## multiverse WILL NOT receive any review or updates from the Ubuntu ## security team. deb http://ports.ubuntu.com/ubuntu-ports/ artful multiverse # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful multiverse deb http://ports.ubuntu.com/ubuntu-ports/ artful-updates multiverse # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful-updates multiverse ## N.B. software from this repository may not have been tested as ## extensively as that contained in the main release, although it includes ## newer versions of some applications which may provide useful features. ## Also, please note that software in backports WILL NOT receive any review ## or updates from the Ubuntu security team. deb http://ports.ubuntu.com/ubuntu-ports/ artful-backports main restricted universe multiverse # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful-backports main restricted universe multiverse ## Uncomment the following two lines to add software from Canonical's ## 'partner' repository. ## This software is not part of Ubuntu, but is offered by Canonical and the ## respective vendors as a service to Ubuntu users. # deb http://archive.canonical.com/ubuntu artful partner # deb-src http://archive.canonical.com/ubuntu artful partner deb http://ports.ubuntu.com/ubuntu-ports/ artful-security main restricted # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful-security main restricted deb http://ports.ubuntu.com/ubuntu-ports/ artful-security universe # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful-security universe deb http://ports.ubuntu.com/ubuntu-ports/ artful-security multiverse # deb-src http://ports.ubuntu.com/ubuntu-ports/ artful-security multiverse