21661037477 has 2 divisors, whose sum is σ = 21661037478. Its totient is φ = 21661037476.

The previous prime is 21661037473. The next prime is 21661037479. The reversal of 21661037477 is 77473016612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12022903201 + 9638134276 = 109649^2 + 98174^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661037477 - 2² = 21661037473 is a prime.

Together with 21661037479, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21661037471) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830518738 + 10830518739.

It is an arithmetic number, because the mean of its divisors is an integer number (10830518739).

Almost surely, 2^21661037477 is an apocalyptic number.

It is an amenable number.

21661037477 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661037477 is an equidigital number, since it uses as much as digits as its factorization.

21661037477 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 296352, while the sum is 44.

The spelling of 21661037477 in words is "twenty-one billion, six hundred sixty-one million, thirty-seven thousand, four hundred seventy-seven".