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Properties of the Number 21978

Twenty-One Thousand Nine Hundred Seventy-Eight

Basics

Value: 21977 → 21978 → 21979

Parity: even

Prime: No

Previous Prime: 21977

Next Prime: 21991

Digit Sum: 27

Digital Root: 9

Palindrome: No

Factorization: 2 × 3 3 × 11 × 37

Divisors: 1, 2, 3, 6, 9, 11, 18, 22, 27, 33

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

2196 Try Today's Challenge

Representations

Binary: 101010111011010

Octal: 52732

Duodecimal: 10876

Hexadecimal: 55da

Square: 483032484

Square Root: 148.24978920727003

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Numbers k such that 4·k = (k written backwards), k > 0. A8918
Numbers n such that two applications of 'Reverse and Subtract' lead to n, whereas one application does not lead to n. A72141
Numbers k such that k written backwards is a nontrivial multiple of k. A8919
Numbers k such that k and 4·k are anagrams. A23088
Non-palindromes in A110751; that is, non-palindromic numbers n such that n and R(n) have the same prime divisors, where R(n) = digit reversal of n. A110819
Nonpalindromic numbers k such that k is not divisible by 10 and k·R(k) is a square, where R(k) is the reversal of k (A004086). A62917
Number of partitions of n with even number (or 0) 2's. A92295
Numbers k such that all the following properties hold: (i) k·reverse(k) is a square; (ii) k ≠ reverse(k); (iii) k and reverse(k) are not both squares; and (iv) k and reverse(k) have the same number of digits. A82994
Non-palindromic numbers n, not divisible by 10, such that either n divides R(n) or R(n) divides n, where R(n) is the digit-reversal of n. A71685
Non-palindromic numbers such that either x=q1.Rev[x] or Rev[x]=q2.x, where R[x]=A004086[x] and q1 or q2 are integers not divisible by 10. A71687