21015778631 has 2 divisors, whose sum is σ = 21015778632. Its totient is φ = 21015778630.

The previous prime is 21015778603. The next prime is 21015778697. The reversal of 21015778631 is 13687751012.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21015778631 is a prime.

It is a super-2 number, since 2×21015778631² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21015778601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10507889315 + 10507889316.

It is an arithmetic number, because the mean of its divisors is an integer number (10507889316).

Almost surely, 2^21015778631 is an apocalyptic number.

21015778631 is a deficient number, since it is larger than the sum of its proper divisors (1).

21015778631 is an equidigital number, since it uses as much as digits as its factorization.

21015778631 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 70560, while the sum is 41.

The spelling of 21015778631 in words is "twenty-one billion, fifteen million, seven hundred seventy-eight thousand, six hundred thirty-one".