21978

Appears in sequences

• Numbers k such that 4*k = (k written backwards), k > 0.at n=1A008918
• Numbers k such that k written backwards is a nontrivial multiple of k.at n=3A008919
• Numbers k such that k and 4*k are anagrams.at n=17A023088
• Least k such that first k terms of A022303 contain n more 2's than 1's.at n=13A025518
• Numbers k such that 2*9^k + 1 is prime.at n=21A056802
• 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).at n=26A062917
• GCD of n! and the reverse of n!.at n=39A071678
• 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.at n=5A071685
• 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.at n=17A071687
• Numbers n such that two applications of 'Reverse and Subtract' lead to n, whereas one application does not lead to n.at n=2A072141
• 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.at n=15A082994
• G.f.: Product((1+x^i)/(1-x^i),i=1..n-1)/(1-x^n), with n = 5.at n=42A091773
• Number of partitions of n with even number (or 0) 2's.at n=40A092295
• 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.at n=7A110819
• a(n) = least non-palindromic k such that k and r(k) have the same n prime divisors, where r(k) is the digit reversal of k.at n=2A110843
• a(n) = 16*n^2 + 2*n.at n=36A158056
• Expansion of g.f. (1-x+2*x^2)/((1-x)*(1-2*x-x^2)).at n=11A174192
• Numbers n with distinct digits such that n divides the reversal of n.at n=11A223081
• Numbers k having at least two complementary pairs of divisors (q, p) and (p', q') such that k = p*q = p'*q' where the decimal digits of p' are the 9's complement of the decimal digits of p and the decimal digits of q' are the 9's complement of the decimal digits of q.at n=13A226587
• Numbers x such that sigma(x) + sigma(R(x)) = sigma(x + R(x)), where R(x) is the digit reversal of x and sigma(x) is the sum of the divisors of x.at n=23A246487