21506220651 has 16 divisors (see below), whose sum is σ = 30365863200. Its totient is φ = 13492259328.

The previous prime is 21506220563. The next prime is 21506220653. The reversal of 21506220651 is 15602260512.

It is not a de Polignac number, because 21506220651 - 2⁷ = 21506220523 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21506220653) 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, 415645 + ... + 464513.

It is an arithmetic number, because the mean of its divisors is an integer number (1897866450).

Almost surely, 2^21506220651 is an apocalyptic number.

21506220651 is a deficient number, since it is larger than the sum of its proper divisors (8859642549).

21506220651 is a wasteful number, since it uses less digits than its factorization.

21506220651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57518.

The product of its (nonzero) digits is 7200, while the sum is 30.

The spelling of 21506220651 in words is "twenty-one billion, five hundred six million, two hundred twenty thousand, six hundred fifty-one".