21177281 has 2 divisors, whose sum is σ = 21177282. Its totient is φ = 21177280.

The previous prime is 21177271. The next prime is 21177287. The reversal of 21177281 is 18277112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18879025 + 2298256 = 4345^2 + 1516^2 .

It is a cyclic number.

It is not a de Polignac number, because 21177281 - 2¹⁰ = 21176257 is a prime.

It is a super-2 number, since 2×21177281² = 896954461105922, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21177287) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10588640 + 10588641.

It is an arithmetic number, because the mean of its divisors is an integer number (10588641).

Almost surely, 2^21177281 is an apocalyptic number.

It is an amenable number.

21177281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21177281 is an equidigital number, since it uses as much as digits as its factorization.

21177281 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1568, while the sum is 29.

The square root of 21177281 is about 4601.8779862139. The cubic root of 21177281 is about 276.6666000548. Note that the first 4 decimals are identical.

The spelling of 21177281 in words is "twenty-one million, one hundred seventy-seven thousand, two hundred eighty-one".