21156653621 has 2 divisors, whose sum is σ = 21156653622. Its totient is φ = 21156653620.

The previous prime is 21156653593. The next prime is 21156653641. The reversal of 21156653621 is 12635665112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18860902225 + 2295751396 = 137335^2 + 47914^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21156653621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21156653641) 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, 10578326810 + 10578326811.

It is an arithmetic number, because the mean of its divisors is an integer number (10578326811).

Almost surely, 2^21156653621 is an apocalyptic number.

It is an amenable number.

21156653621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21156653621 is an equidigital number, since it uses as much as digits as its factorization.

21156653621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 64800, while the sum is 38.

The spelling of 21156653621 in words is "twenty-one billion, one hundred fifty-six million, six hundred fifty-three thousand, six hundred twenty-one".