20910

Appears in sequences

• Coefficients of expansion of Jacobi nome q in certain powers of (1/2)*(1 - sqrt(k')) / (1 + sqrt(k')).at n=5A002103
• Number of 2-connected claw-free graphs on n nodes.at n=9A022563
• Number of partitions of n into parts not of the form 21k, 21k+5 or 21k-5. Also number of partitions with at most 4 parts of size 1 and differences between parts at distance 9 are greater than 1.at n=39A035983
• Base-9 palindromes that start with 3.at n=35A043030
• Numbers whose base-12 representation has exactly 5 runs.at n=16A043654
• 55 'Reverse and Add' steps are needed to reach a palindrome.at n=2A065322
• Triangular numbers whose index is a multiple of the sum of their digits.at n=36A067520
• Numbers k such that phi(k) = bigomega(k)*tau(k)^2.at n=28A068540
• Triangular numbers of the form 10*k.at n=41A069498
• Triangular numbers with internal digits also forming a triangular number.at n=33A069702
• Products of members of pairs in A075333.at n=35A075337
• Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=6.at n=35A076672
• Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=7.at n=31A076673
• Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=10.at n=31A076675
• Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=11.at n=29A076676
• Triangular numbers which are also happy numbers (cf. A007770).at n=30A076712
• Triangular numbers with square pyramidal indices.at n=8A076767
• Triangular numbers whose internal digits form a triangular number. Or triangular number such that deleting the MSD and LSD leaves a triangular number.at n=47A077366
• Positive square-root of terms of the self-convolution of A087150.at n=36A087151
• Common differences of arithmetic progressions in A086786.at n=20A087310