145721921 has 4 divisors (see below), whose sum is σ = 146001072. Its totient is φ = 145442772.

The previous prime is 145721903. The next prime is 145721923. The reversal of 145721921 is 129127541.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 129127541 = 2053 ⋅62897.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-145721921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (145721923) 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, 138791 + ... + 139836.

It is an arithmetic number, because the mean of its divisors is an integer number (36500268).

Almost surely, 2^145721921 is an apocalyptic number.

It is an amenable number.

145721921 is a deficient number, since it is larger than the sum of its proper divisors (279151).

145721921 is an equidigital number, since it uses as much as digits as its factorization.

145721921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 279150.

The product of its digits is 5040, while the sum is 32.

The square root of 145721921 is about 12071.5334982760. The cubic root of 145721921 is about 526.2292236820.

The spelling of 145721921 in words is "one hundred forty-five million, seven hundred twenty-one thousand, nine hundred twenty-one".