21261036787 has 4 divisors (see below), whose sum is σ = 21264886296. Its totient is φ = 21257187280.

The previous prime is 21261036779. The next prime is 21261036809. The reversal of 21261036787 is 78763016212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21261036787 - 2³ = 21261036779 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21261036707) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1916458 + ... + 1927519.

It is an arithmetic number, because the mean of its divisors is an integer number (5316221574).

Almost surely, 2^21261036787 is an apocalyptic number.

21261036787 is a deficient number, since it is larger than the sum of its proper divisors (3849509).

21261036787 is an equidigital number, since it uses as much as digits as its factorization.

21261036787 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3849508.

The product of its (nonzero) digits is 169344, while the sum is 43.

The spelling of 21261036787 in words is "twenty-one billion, two hundred sixty-one million, thirty-six thousand, seven hundred eighty-seven".