645956981 has 8 divisors (see below), whose sum is σ = 653063424. Its totient is φ = 638866800.

The previous prime is 645956977. The next prime is 645957019. The reversal of 645956981 is 189659546.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 645956981 - 2² = 645956977 is a prime.

It is a super-3 number, since 3×645956981³ (a number of 27 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645956921) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 86756 + ... + 93906.

It is an arithmetic number, because the mean of its divisors is an integer number (81632928).

Almost surely, 2^645956981 is an apocalyptic number.

It is an amenable number.

645956981 is a deficient number, since it is larger than the sum of its proper divisors (7106443).

645956981 is a wasteful number, since it uses less digits than its factorization.

645956981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8131.

The product of its digits is 2332800, while the sum is 53.

The square root of 645956981 is about 25415.6837602296. The cubic root of 645956981 is about 864.4393578209.

The spelling of 645956981 in words is "six hundred forty-five million, nine hundred fifty-six thousand, nine hundred eighty-one".