21640477 has 2 divisors, whose sum is σ = 21640478. Its totient is φ = 21640476.

The previous prime is 21640471. The next prime is 21640499. The reversal of 21640477 is 77404612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11329956 + 10310521 = 3366^2 + 3211^2 .

It is a cyclic number.

It is not a de Polignac number, because 21640477 - 2³ = 21640469 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21640471) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10820238 + 10820239.

It is an arithmetic number, because the mean of its divisors is an integer number (10820239).

Almost surely, 2^21640477 is an apocalyptic number.

It is an amenable number.

21640477 is a deficient number, since it is larger than the sum of its proper divisors (1).

21640477 is an equidigital number, since it uses as much as digits as its factorization.

21640477 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 9408, while the sum is 31.

The square root of 21640477 is about 4651.9326091421. The cubic root of 21640477 is about 278.6691821986.

The spelling of 21640477 in words is "twenty-one million, six hundred forty thousand, four hundred seventy-seven".