123256

Appears in sequences

• Doubly triangular numbers: a(n) = n*(n+1)*(n^2+n+2)/8.at n=31A002817
• Smallest number which is the sum of two positive triangular numbers in exactly n different ways.at n=11A052346
• Length of period of continued fraction expansion of square root of 3^n-1.at n=22A062345
• Triangular numbers whose reverse is prime.at n=25A066751
• Smallest triangular number which begins with the concatenation of first n natural numbers.at n=2A077692
• Numbers of the form prime(n) + prime(n+1) - 2 that are also triangular numbers, T(k) = k(k+1)/2.at n=36A110891
• Triangular numbers whose digit reversal is prime; trailing zeros are permitted.at n=33A115704
• Numbers that have exactly 7 representations as a k-gonal number, P(n,k) = n*((k-2)*n - (k-4))/2, k and n >= 3.at n=28A321157
• a(n) is the smallest nonnegative integer that can be written as a sum of two distinct nonzero triangular numbers in exactly n ways or -1 if no such integer exists.at n=11A342326