21211166621 has 2 divisors, whose sum is σ = 21211166622. Its totient is φ = 21211166620.

The previous prime is 21211166593. The next prime is 21211166719. The reversal of 21211166621 is 12666111212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21138252100 + 72914521 = 145390^2 + 8539^2 .

It is a cyclic number.

It is not a de Polignac number, because 21211166621 - 2¹⁰ = 21211165597 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21211156621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605583310 + 10605583311.

It is an arithmetic number, because the mean of its divisors is an integer number (10605583311).

Almost surely, 2^21211166621 is an apocalyptic number.

It is an amenable number.

21211166621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21211166621 is an equidigital number, since it uses as much as digits as its factorization.

21211166621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1728, while the sum is 29.

Adding to 21211166621 its reverse (12666111212), we get a palindrome (33877277833).

The spelling of 21211166621 in words is "twenty-one billion, two hundred eleven million, one hundred sixty-six thousand, six hundred twenty-one".