21506216655 has 32 divisors (see below), whose sum is σ = 42900715008. Its totient is φ = 8937648000.

The previous prime is 21506216621. The next prime is 21506216657. The reversal of 21506216655 is 55661260512.

It is a happy number.

It is not a de Polignac number, because 21506216655 - 2⁹ = 21506216143 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506216657) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 9308896 + ... + 9311205.

It is an arithmetic number, because the mean of its divisors is an integer number (1340647344).

Almost surely, 2^21506216655 is an apocalyptic number.

21506216655 is a deficient number, since it is larger than the sum of its proper divisors (21394498353).

21506216655 is a wasteful number, since it uses less digits than its factorization.

21506216655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18620127.

The product of its (nonzero) digits is 108000, while the sum is 39.

The spelling of 21506216655 in words is "twenty-one billion, five hundred six million, two hundred sixteen thousand, six hundred fifty-five".