Things Mathematical

• American Mathematical Society
• Towson Number Theory Seminar
• MASON: The Mid-Atlantic Seminar On Numbers
• MathSciNet (Mathematical Reviews online—subscription required)
• Number Theory Web

Things Computational

• MiKTeX (an excellent TeX system for Windows)
• Overleaf (still free LaTeX in the cloud)
• W3Schools (Online tutorials and examples on HTML, CSS, etc.)