21012

Appears in sequences

• Number of collinear point-triples in an n X n grid.at n=13A000938
• n written in fractional base 3/2.at n=17A024629
• Even palindromes in which parity of digits alternates.at n=25A030149
• Base-10 palindromes that start with 2.at n=32A043037
• Palindromic and divisible by 4.at n=45A045639
• Palindromes that are divisible by 6.at n=32A045641
• Star of David matchstick numbers: a(n) = 6*n*(3*n+1).at n=34A045946
• Palindromic even lucky numbers.at n=26A045960
• Palindromes with exactly 5 prime factors (counted with multiplicity).at n=27A046331
• Composite palindromes whose sum of prime factors is prime (counted with multiplicity).at n=45A046365
• a(n) = smallest palindrome > a(n-1) such that a(1)*a(2)*...*a(n) + 1 is prime with a(1) = 2.at n=23A051896
• Palindromes divisible by their digit sum.at n=45A082232
• a(n) = T(n) concatenated with reverse(T(n)) divided by 11, where T(n) is the n-th triangular number.at n=21A084008
• Palindromes with more than 3 digits in which the absolute difference of a pair of successive digits is identical.at n=24A085109
• a(n) = floor(2^n*log(n)).at n=12A094939
• Binary numbers with 2 replacing 1 in odd positions.at n=27A095914
• Palindromic in bases 10 and 32.at n=24A099165
• Number of partitions of 2n in which both odd parts and parts that are multiples of 3 occur with even multiplicities. There is no restriction on the other even parts.at n=26A101230
• The n-th row of the following array contains all palindromes, with at most n digits, with digit sum n. Sequence contains the array by rows.at n=29A109858
• Palindromes sandwiched between twin primes.at n=6A113838