21006400664 has 32 divisors (see below), whose sum is σ = 41773263840. Its totient is φ = 9881836800.

The previous prime is 21006400661. The next prime is 21006400673. The reversal of 21006400664 is 46600460012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006400661) 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, 924557 + ... + 947004.

It is an arithmetic number, because the mean of its divisors is an integer number (1305414495).

Almost surely, 2^21006400664 is an apocalyptic number.

It is an amenable number.

21006400664 is a deficient number, since it is larger than the sum of its proper divisors (20766863176).

21006400664 is a wasteful number, since it uses less digits than its factorization.

21006400664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1871651 (or 1871647 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 29.

Adding to 21006400664 its reverse (46600460012), we get a palindrome (67606860676).

The spelling of 21006400664 in words is "twenty-one billion, six million, four hundred thousand, six hundred sixty-four".