21261216512664 has 64 divisors (see below), whose sum is σ = 59722518348000. Its totient is φ = 7007442140160.

The previous prime is 21261216512663. The next prime is 21261216512761. The reversal of 21261216512664 is 46621561216212.

21261216512664 is a `hidden beast` number, since 2 + 1 + 2 + 6 + 121 + 6 + 512 + 6 + 6 + 4 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21261216512663) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 552967057 + ... + 553005504.

Almost surely, 2^{21261216512664} is an apocalyptic number.

21261216512664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21261216512664 is an abundant number, since it is smaller than the sum of its proper divisors (38461301835336).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21261216512664 is a wasteful number, since it uses less digits than its factorization.

21261216512664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1105972665 (or 1105972655 counting only the distinct ones).

The product of its digits is 414720, while the sum is 45.

Adding to 21261216512664 its reverse (46621561216212), we get a palindrome (67882777728876).

The spelling of 21261216512664 in words is "twenty-one trillion, two hundred sixty-one billion, two hundred sixteen million, five hundred twelve thousand, six hundred sixty-four".