21001211977 has 2 divisors, whose sum is σ = 21001211978. Its totient is φ = 21001211976.

The previous prime is 21001211969. The next prime is 21001212007. The reversal of 21001211977 is 77911210012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20979784336 + 21427641 = 144844^2 + 4629^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001211977 - 2³ = 21001211969 is a prime.

It is not a weakly prime, because it can be changed into another prime (21001211377) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500605988 + 10500605989.

It is an arithmetic number, because the mean of its divisors is an integer number (10500605989).

Almost surely, 2^21001211977 is an apocalyptic number.

It is an amenable number.

21001211977 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001211977 is an equidigital number, since it uses as much as digits as its factorization.

21001211977 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1764, while the sum is 31.

Adding to 21001211977 its reverse (77911210012), we get a palindrome (98912421989).

The spelling of 21001211977 in words is "twenty-one billion, one million, two hundred eleven thousand, nine hundred seventy-seven".