21019681021 has 2 divisors, whose sum is σ = 21019681022. Its totient is φ = 21019681020.

The previous prime is 21019680989. The next prime is 21019681043. The reversal of 21019681021 is 12018691012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19116104121 + 1903576900 = 138261^2 + 43630^2 .

It is a cyclic number.

It is not a de Polignac number, because 21019681021 - 2⁵ = 21019680989 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21019681091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10509840510 + 10509840511.

It is an arithmetic number, because the mean of its divisors is an integer number (10509840511).

Almost surely, 2^21019681021 is an apocalyptic number.

It is an amenable number.

21019681021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21019681021 is an equidigital number, since it uses as much as digits as its factorization.

21019681021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1728, while the sum is 31.

Subtracting from 21019681021 its reverse (12018691012), we obtain a palindrome (9000990009).

The spelling of 21019681021 in words is "twenty-one billion, nineteen million, six hundred eighty-one thousand, twenty-one".