21221501551 has 2 divisors, whose sum is σ = 21221501552. Its totient is φ = 21221501550.

The previous prime is 21221501549. The next prime is 21221501579. The reversal of 21221501551 is 15510512212.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21221501551 - 2¹ = 21221501549 is a prime.

Together with 21221501549, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21221501501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610750775 + 10610750776.

It is an arithmetic number, because the mean of its divisors is an integer number (10610750776).

Almost surely, 2^21221501551 is an apocalyptic number.

21221501551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221501551 is an equidigital number, since it uses as much as digits as its factorization.

21221501551 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1000, while the sum is 25.

The spelling of 21221501551 in words is "twenty-one billion, two hundred twenty-one million, five hundred one thousand, five hundred fifty-one".