23871

Appears in sequences

• In A015922, not in A033553.at n=31A033554
• Triangular numbers with sum of digits = 21.at n=18A068131
• Triangular numbers of the form k^2 + k + 1.at n=6A069017
• Triangular numbers whose sum of aliquot divisors is a prime number.at n=18A083676
• Triangular numbers for which the sum of the digits is an octagonal number.at n=21A117523
• Triangular numbers t which are average of two consecutive primes p and p+4.at n=25A129752
• a(n) is the smallest number k larger than a(n-1) such that n*d(k)*sopf(k)=sigma(k), where d is the number of divisors (A000005) and sopf the sum of prime factors without repetition (A008472).at n=21A134382
• Number of n X n binary arrays symmetric about both diagonal and antidiagonal with all ones connected only in a 1010-1111-0101 pattern in any orientation.at n=18A147432
• Triangular numbers T such that T+2 is a prime.at n=40A171570
• Triangular numbers which have one or more occurrences of exactly five different digits.at n=12A241788
• Triangular numbers representable as x*y+x+y such that x and y are triangular numbers, x>=y>0.at n=21A259745
• Triangular numbers that are repdigits with length > 2 in some base.at n=20A274084
• The first of three consecutive triangular numbers the sum of which is equal to the sum of three consecutive primes.at n=20A298168
• E.g.f. A(x) = 3 + Integral B(x)*C(x) dx such that C(x)^2 - A(x)^2 = 16 and B(x)^2 - A(x)^2 = 7.at n=4A323563
• a(n) is the least integer k such that sigma(k)/(d(k)*sopf(k)) = n where d=A000005, sigma=A000203 and sopf=A008472.at n=21A328174
• Number of sets of distinct positive integers whose sum of squares is a square, the largest integer of a set is n.at n=21A339612
• G.f. satisfies A(x) = 1 + x*A(x)^2 + x^3*A(x).at n=10A367056