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Properties of the Number 21788

Twenty-One Thousand Seven Hundred Eighty-Eight

Basics

Value: 21787 → 21788 → 21789

Parity: even

Prime: No

Previous Prime: 21787

Next Prime: 21799

Digit Sum: 26

Digital Root: 8

Palindrome: No

Factorization: 2 2 × 13 × 419

Divisors: 1, 2, 4, 13, 26, 52, 419, 838, 1676, 5447

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

2196 Try Today's Challenge

Representations

Binary: 101010100011100

Octal: 52434

Duodecimal: 10738

Hexadecimal: 551c

Square: 474716944

Square Root: 147.60758788084033

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

Smallest k > 0 with gcd(k, rev(k)) = n, where rev(k) is digit reversal of k, or 0 if no such k exists. A69554
G.f. satisfies: A(x) = 1 + x·A(x)2 + 2·x2*(A(x)2 - A(x)); equals the base sequence of pendular trinomial triangle A122445. A122446
Column 3 of array in A226513. A226514
a(n) = 1·t(n) + 2·t(n-1) + ...+ k·t(n+1-k), where k=floor((n+1)/2) and t is A001950 (upper Wythoff sequence). A23867
Values of n such that prime(n) does not divide any 10-digit pandigital number (i.e. any value in A050278). A292703
If p(x) is the x-th prime, then the n-th set of 4 consecutive sexy prime pairs starts at p(a(n)). A95963
The number of unigraphical partitions of 2m; that is, the number of partitions of 2m which are realizable as the degree sequence of one and only one graph (where loops are not allowed but multiple edges are allowed). A143981
a(n) gives the number of nonisomorphic connected compact Lie groups of dimension n which are simple products. A177821
Pendular trinomial triangle, read by rows of 2n+1 terms (n>=0), defined by the recurrence: if 0 < k < n, T(n,k) = T(n-1,k) + 2·T(n,2n-1-k); otherwise, if n-1 < k < 2n-1, T(n,k) = T(n-1,k) + T(n,2n-2-k); with T(n,0) = T(n+1,2n) = 1 and T(n+1,2n+1) = T(n+1,2n+2) = 0. A122445
Decimal expansion of 1/784. A21788