21581557651 has 2 divisors, whose sum is σ = 21581557652. Its totient is φ = 21581557650.

The previous prime is 21581557609. The next prime is 21581557687. The reversal of 21581557651 is 15675518512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21581557651 - 2⁷ = 21581557523 is a prime.

It is not a weakly prime, because it can be changed into another prime (21581557051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10790778825 + 10790778826.

It is an arithmetic number, because the mean of its divisors is an integer number (10790778826).

Almost surely, 2^21581557651 is an apocalyptic number.

21581557651 is a deficient number, since it is larger than the sum of its proper divisors (1).

21581557651 is an equidigital number, since it uses as much as digits as its factorization.

21581557651 is an evil number, because the sum of its binary digits is even.

The product of its digits is 420000, while the sum is 46.

The spelling of 21581557651 in words is "twenty-one billion, five hundred eighty-one million, five hundred fifty-seven thousand, six hundred fifty-one".