21212

Appears in sequences

• Coordination sequence for squashed {D_5}* lattice, perhaps the smallest example of a "non-superficial" lattice.at n=9A010024
• Two-bell analog of A028355.at n=7A028359
• Even palindromes in which parity of digits alternates.at n=26A030149
• Base-2 digital convolution sequence.at n=41A033639
• Triangle of coefficients of generating function of 4-ary rooted trees of height at most n.at n=54A036606
• Number of 4-ary rooted trees with n nodes and height at most 4.at n=23A036609
• Number of 4-ary rooted trees with n nodes and height exactly 4.at n=23A036628
• Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1.at n=4A037495
• Base-10 palindromes that start with 2.at n=34A043037
• Palindromic and divisible by 4.at n=47A045639
• Numbers k such that k^2 contains only digits {4,8,9}.at n=9A053966
• Numbers whose product of decimal digits equals its sum of binary digits.at n=29A064003
• Numbers n whose sum of divisors and number of divisors are both triangular numbers.at n=40A070996
• Palindromic even numbers with exactly 3 prime factors (counted with multiplicity).at n=29A075816
• Palindromes whose product of digits is a positive palindrome.at n=46A082207
• In the array shown below the n-th row contains all the palindromes that use digits > 0 and have a digit sum of n. The sequence contains the array read by rows.at n=39A082266
• Palindromes in A082939.at n=19A082940
• Palindromes in A083114.at n=38A083115
• Palindromes with more than 3 digits in which the absolute difference of a pair of successive digits is identical.at n=25A085109
• Palindromes in which the sum of the internal digits = the sum of the external digits.at n=16A088285