21720277 has 2 divisors, whose sum is σ = 21720278. Its totient is φ = 21720276.

The previous prime is 21720247. The next prime is 21720311. The reversal of 21720277 is 77202712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14676561 + 7043716 = 3831^2 + 2654^2 .

It is a cyclic number.

It is not a de Polignac number, because 21720277 - 2¹⁹ = 21195989 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21720247) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10860138 + 10860139.

It is an arithmetic number, because the mean of its divisors is an integer number (10860139).

Almost surely, 2^21720277 is an apocalyptic number.

It is an amenable number.

21720277 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720277 is an equidigital number, since it uses as much as digits as its factorization.

21720277 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2744, while the sum is 28.

The square root of 21720277 is about 4660.5017970171. The cubic root of 21720277 is about 279.0112960745.

Adding to 21720277 its reverse (77202712), we get a palindrome (98922989).

The spelling of 21720277 in words is "twenty-one million, seven hundred twenty thousand, two hundred seventy-seven".