64991621 has 4 divisors (see below), whose sum is σ = 66217932. Its totient is φ = 63765312.

The previous prime is 64991617. The next prime is 64991623. The reversal of 64991621 is 12619946.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12619946 = 2 ⋅6309973.

It can be written as a sum of positive squares in 2 ways, for example, as 32615521 + 32376100 = 5711^2 + 5690^2 .

It is a cyclic number.

It is not a de Polignac number, because 64991621 - 2² = 64991617 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 (64991623) 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, 613076 + ... + 613181.

It is an arithmetic number, because the mean of its divisors is an integer number (16554483).

Almost surely, 2^64991621 is an apocalyptic number.

It is an amenable number.

64991621 is a deficient number, since it is larger than the sum of its proper divisors (1226311).

64991621 is a wasteful number, since it uses less digits than its factorization.

64991621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1226310.

The product of its digits is 23328, while the sum is 38.

The square root of 64991621 is about 8061.7380880304. The cubic root of 64991621 is about 402.0552983672.

The spelling of 64991621 in words is "sixty-four million, nine hundred ninety-one thousand, six hundred twenty-one".