21510202421 has 2 divisors, whose sum is σ = 21510202422. Its totient is φ = 21510202420.

The previous prime is 21510202367. The next prime is 21510202429. The reversal of 21510202421 is 12420201512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19795083025 + 1715119396 = 140695^2 + 41414^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21510202421 is a prime.

It is a super-2 number, since 2×21510202421² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21510202393 and 21510202402.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21510202429) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10755101210 + 10755101211.

It is an arithmetic number, because the mean of its divisors is an integer number (10755101211).

Almost surely, 2^21510202421 is an apocalyptic number.

It is an amenable number.

21510202421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21510202421 is an equidigital number, since it uses as much as digits as its factorization.

21510202421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 320, while the sum is 20.

Adding to 21510202421 its reverse (12420201512), we get a palindrome (33930403933).

Subtracting from 21510202421 its reverse (12420201512), we obtain a palindrome (9090000909).

The spelling of 21510202421 in words is "twenty-one billion, five hundred ten million, two hundred two thousand, four hundred twenty-one".