21505221651 has 8 divisors (see below), whose sum is σ = 29920308480. Its totient is φ = 13713474632.

The previous prime is 21505221613. The next prime is 21505221671. The reversal of 21505221651 is 15612250512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21505221651 - 2¹³ = 21505213459 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21505221671) 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, 155834871 + ... + 155835008.

It is an arithmetic number, because the mean of its divisors is an integer number (3740038560).

Almost surely, 2^21505221651 is an apocalyptic number.

21505221651 is a deficient number, since it is larger than the sum of its proper divisors (8415086829).

21505221651 is a wasteful number, since it uses less digits than its factorization.

21505221651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 311669905.

The product of its (nonzero) digits is 6000, while the sum is 30.

The spelling of 21505221651 in words is "twenty-one billion, five hundred five million, two hundred twenty-one thousand, six hundred fifty-one".