21521620987 has 2 divisors, whose sum is σ = 21521620988. Its totient is φ = 21521620986.

The previous prime is 21521620961. The next prime is 21521621047. The reversal of 21521620987 is 78902612512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21521620987 - 2³¹ = 19374137339 is a prime.

It is not a weakly prime, because it can be changed into another prime (21521621987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760810493 + 10760810494.

It is an arithmetic number, because the mean of its divisors is an integer number (10760810494).

Almost surely, 2^21521620987 is an apocalyptic number.

21521620987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21521620987 is an equidigital number, since it uses as much as digits as its factorization.

21521620987 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 120960, while the sum is 43.

The spelling of 21521620987 in words is "twenty-one billion, five hundred twenty-one million, six hundred twenty thousand, nine hundred eighty-seven".