18981

Appears in sequences

• Numbers k such that k divides s(k), where s(1)=1, s(j)= s(j-1) + j*7^(j-1).at n=27A014948
• Odd 9-gonal (or enneagonal) numbers.at n=37A028991
• Cubeful (i.e., not cubefree) palindromes.at n=30A035133
• Palindromic and divisible by 9.at n=32A045644
• Palindromes with exactly 5 prime factors (counted with multiplicity).at n=24A046331
• a(n) = n*(2*n+5)*(n-1)/6.at n=38A051925
• Numbers k such that phi(k)/lambda(k) increases to a record value, where phi(k) is the Euler totient function (A000010) and lambda(k) is the Carmichael lambda function (A002322).at n=17A066605
• q-factorial numbers 3!_q.at n=26A069778
• Palindromes divisible by their digit sum.at n=40A082232
• Palindromic nonagonal (or 9-gonal or enneagonal) numbers.at n=6A082723
• a(n) is the odd-length palindrome whose digits up to the center are those of n and whose center digit is equal to the digital root of the product of the factorial of n and the reverse of n.at n=17A082941
• a(n) = concatenate(n, A010888(2*n), reverse(n)), where A010888 = digital root.at n=17A082944
• Palindromes arising in A083125. a(n) = A083125(n)*A083125(n+1).at n=40A083126
• Diagonal of A083464.at n=12A083465
• Palindromes n such that 10n01 is a prime.at n=31A099744
• Consider all (2n+1)-digit palindromic primes of the form 10...0M0...01 (so that M is a palindrome with <= 2n-1 digits); a(n) = smallest such M.at n=53A100026
• Enneagonal numbers divisible by 9.at n=17A117796
• a(0) = 0, a(1) = 1; for n>0, a(2*n) = 3*a(2*n-1), a(2*n+1) = 3*a(2*n) - 2*a(n-1).at n=10A129770
• Number of nX2 1..3 arrays containing at least one of each value, all equal values connected, rows considered as a single number in nondecreasing order, and columns considered as a single number in nondecreasing order.at n=19A166796
• Palindromic mountain numbers.at n=36A173070