21377561 has 2 divisors, whose sum is σ = 21377562. Its totient is φ = 21377560.

The previous prime is 21377549. The next prime is 21377567. The reversal of 21377561 is 16577312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19891600 + 1485961 = 4460^2 + 1219^2 .

It is a cyclic number.

It is not a de Polignac number, because 21377561 - 2¹⁸ = 21115417 is a prime.

It is a super-2 number, since 2×21377561² = 914000228617442, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21377567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10688780 + 10688781.

It is an arithmetic number, because the mean of its divisors is an integer number (10688781).

Almost surely, 2^21377561 is an apocalyptic number.

It is an amenable number.

21377561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21377561 is an equidigital number, since it uses as much as digits as its factorization.

21377561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8820, while the sum is 32.

The square root of 21377561 is about 4623.5874599709. The cubic root of 21377561 is about 277.5360383897.

The spelling of 21377561 in words is "twenty-one million, three hundred seventy-seven thousand, five hundred sixty-one".