645581551 has 4 divisors (see below), whose sum is σ = 647160400. Its totient is φ = 644002704.

The previous prime is 645581533. The next prime is 645581567. The reversal of 645581551 is 155185546.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 645581551 - 2⁷ = 645581423 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 (645581051) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 788811 + ... + 789628.

It is an arithmetic number, because the mean of its divisors is an integer number (161790100).

Almost surely, 2^645581551 is an apocalyptic number.

645581551 is a deficient number, since it is larger than the sum of its proper divisors (1578849).

645581551 is a wasteful number, since it uses less digits than its factorization.

645581551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1578848.

The product of its digits is 120000, while the sum is 40.

The square root of 645581551 is about 25408.2968929442. The cubic root of 645581551 is about 864.2718547356.

The spelling of 645581551 in words is "six hundred forty-five million, five hundred eighty-one thousand, five hundred fifty-one".