21515523403991 has 2 divisors, whose sum is σ = 21515523403992. Its totient is φ = 21515523403990.

The previous prime is 21515523403987. The next prime is 21515523404021. The reversal of 21515523403991 is 19930432551512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21515523403991 - 2² = 21515523403987 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21515523403921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10757761701995 + 10757761701996.

It is an arithmetic number, because the mean of its divisors is an integer number (10757761701996).

Almost surely, 2^{21515523403991} is an apocalyptic number.

21515523403991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21515523403991 is an equidigital number, since it uses as much as digits as its factorization.

21515523403991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1458000, while the sum is 50.

The spelling of 21515523403991 in words is "twenty-one trillion, five hundred fifteen billion, five hundred twenty-three million, four hundred three thousand, nine hundred ninety-one".