Divisor and totient functions

σ, τ, φ, Jordan and Dedekind ψ, unitary and biunitary divisors, gcd-sums, Ramanujan sums, totient multiplicities and values.

Part 1 of 2

• Alder's totient function
• Average and divisibility of the divisor sum
• Dedekind psi function
• Divisor-power sums
• Divisors in short intervals
• Euler's function and divisor sums along linear recurrences
• Gaps between divisors
• Jordan's totient function
• Liouville's divisor-function identity
• Nicol numbers
• Parity of divisor counts
• Pillai's gcd-sum function
• Ramanujan sums
• Residues of rounded quotients n/k
• Totient of the sum of divisors
• Unitary divisors
• Biunitary divisors
• Regular integers modulo n
• Values of n + φ(n)
• Ford's theorem on totient multiplicities

Part 2 of 2

• Gronwall's theorem
• Relatively prime subset counts

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