21235756642 has 4 divisors (see below), whose sum is σ = 31853634966. Its totient is φ = 10617878320.

The previous prime is 21235756639. The next prime is 21235756673. The reversal of 21235756642 is 24665753212.

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

It can be written as a sum of positive squares in only one way, i.e., 21167049121 + 68707521 = 145489^2 + 8289^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5308939159 + ... + 5308939162.

Almost surely, 2^21235756642 is an apocalyptic number.

21235756642 is a deficient number, since it is larger than the sum of its proper divisors (10617878324).

21235756642 is a wasteful number, since it uses less digits than its factorization.

21235756642 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10617878323.

The product of its digits is 604800, while the sum is 43.

The spelling of 21235756642 in words is "twenty-one billion, two hundred thirty-five million, seven hundred fifty-six thousand, six hundred forty-two".