661720519 has 4 divisors (see below), whose sum is σ = 661795344. Its totient is φ = 661645696.

The previous prime is 661720487. The next prime is 661720531. The reversal of 661720519 is 915027166.

661720519 = T₂₁₀₀₂ + T₂₁₀₀₃ + T₂₁₀₀₄.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 661720519 - 2⁵ = 661720487 is a prime.

It is a super-2 number, since 2×661720519² = 875748090531258722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661721519) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22042 + ... + 42535.

It is an arithmetic number, because the mean of its divisors is an integer number (165448836).

Almost surely, 2^661720519 is an apocalyptic number.

661720519 is the 21004-th centered triangular number.

661720519 is a deficient number, since it is larger than the sum of its proper divisors (74825).

661720519 is a wasteful number, since it uses less digits than its factorization.

661720519 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 74824.

The product of its (nonzero) digits is 22680, while the sum is 37.

The square root of 661720519 is about 25723.9289184215. The cubic root of 661720519 is about 871.4146707154.

The spelling of 661720519 in words is "six hundred sixty-one million, seven hundred twenty thousand, five hundred nineteen".