21206124664 has 8 divisors (see below), whose sum is σ = 39761483760. Its totient is φ = 10603062328.

The previous prime is 21206124587. The next prime is 21206124671. The reversal of 21206124664 is 46642160212.

It is a tau number, because it is divible by the number of its divisors (8).

It is a super-2 number, since 2×21206124664² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1325382784 + ... + 1325382799.

It is an arithmetic number, because the mean of its divisors is an integer number (4970185470).

Almost surely, 2^21206124664 is an apocalyptic number.

It is an amenable number.

21206124664 is a deficient number, since it is larger than the sum of its proper divisors (18555359096).

21206124664 is a wasteful number, since it uses less digits than its factorization.

21206124664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2650765589 (or 2650765585 counting only the distinct ones).

The product of its (nonzero) digits is 27648, while the sum is 34.

Adding to 21206124664 its reverse (46642160212), we get a palindrome (67848284876).

The spelling of 21206124664 in words is "twenty-one billion, two hundred six million, one hundred twenty-four thousand, six hundred sixty-four".