21406556377 has 2 divisors, whose sum is σ = 21406556378. Its totient is φ = 21406556376.

The previous prime is 21406556329. The next prime is 21406556407. The reversal of 21406556377 is 77365560412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12931328656 + 8475227721 = 113716^2 + 92061^2 .

It is a cyclic number.

It is not a de Polignac number, because 21406556377 - 2¹¹ = 21406554329 is a prime.

It is a super-2 number, since 2×21406556377² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21406536377) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10703278188 + 10703278189.

It is an arithmetic number, because the mean of its divisors is an integer number (10703278189).

Almost surely, 2^21406556377 is an apocalyptic number.

It is an amenable number.

21406556377 is a deficient number, since it is larger than the sum of its proper divisors (1).

21406556377 is an equidigital number, since it uses as much as digits as its factorization.

21406556377 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1058400, while the sum is 46.

The spelling of 21406556377 in words is "twenty-one billion, four hundred six million, five hundred fifty-six thousand, three hundred seventy-seven".