661821487 has 4 divisors (see below), whose sum is σ = 662333056. Its totient is φ = 661309920.

The previous prime is 661821463. The next prime is 661821493. The reversal of 661821487 is 784128166.

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 661821487 - 2⁷ = 661821359 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 (661821497) 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, 253839 + ... + 256432.

It is an arithmetic number, because the mean of its divisors is an integer number (165583264).

Almost surely, 2^661821487 is an apocalyptic number.

661821487 is a deficient number, since it is larger than the sum of its proper divisors (511569).

661821487 is a wasteful number, since it uses less digits than its factorization.

661821487 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 511568.

The product of its digits is 129024, while the sum is 43.

The square root of 661821487 is about 25725.8913742556. The cubic root of 661821487 is about 871.4589897893.

The spelling of 661821487 in words is "six hundred sixty-one million, eight hundred twenty-one thousand, four hundred eighty-seven".