125661509 has 4 divisors (see below), whose sum is σ = 129057804. Its totient is φ = 122265216.

The previous prime is 125661493. The next prime is 125661517. The reversal of 125661509 is 905166521.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 905166521 = 7 ⋅129309503.

It can be written as a sum of positive squares in 2 ways, for example, as 89397025 + 36264484 = 9455^2 + 6022^2 .

It is a cyclic number.

It is not a de Polignac number, because 125661509 - 2⁴ = 125661493 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (125661559) 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, 1698092 + ... + 1698165.

It is an arithmetic number, because the mean of its divisors is an integer number (32264451).

Almost surely, 2^125661509 is an apocalyptic number.

It is an amenable number.

125661509 is a deficient number, since it is larger than the sum of its proper divisors (3396295).

125661509 is an equidigital number, since it uses as much as digits as its factorization.

125661509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3396294.

The product of its (nonzero) digits is 16200, while the sum is 35.

The square root of 125661509 is about 11209.8844329458. The cubic root of 125661509 is about 500.8804606680.

The spelling of 125661509 in words is "one hundred twenty-five million, six hundred sixty-one thousand, five hundred nine".