78210

Appears in sequences

• Triangular numbers such that both the number formed by the first floor((k+1)/2) digits and the remaining part (if any) are triangular numbers, where k is the number of digits.at n=15A068821
• Numbers k such that both k and 2*k are balanced numbers (A020492).at n=38A076375
• Numbers k such that k, 2*k and 4*k are balanced numbers (A020492).at n=19A076376
• Numbers n such that sigma(n) = 12*phi(n).at n=11A104902
• Triangular numbers that are sums of two consecutive primes.at n=39A111163
• Numbers that cannot be expressed as a sum of 2 triangular numbers and a power of 2.at n=15A112665
• Triangular numbers that are sandwiched between two semiprimes; or triangular numbers t such that t-1 and t+1 are both semiprime.at n=21A121898
• Triangular numbers whose sum of triangular divisors is also triangular and greater than 1.at n=4A209310
• Smallest triangular number whose decimal expansion ends (nontrivially) with the n-th triangular number.at n=19A229262
• Number of partitions of n such that (greatest part) + (least part) > number of parts.at n=47A237870
• Triangular numbers that are sandwiched between two squarefree semiprimes.at n=19A375384