20706

Appears in sequences

• Coordination sequence for MgZn2, Position Zn2.at n=36A009938
• Number of directed site animals with no loops enumerated by area (or number of sites).at n=11A010374
• a(n) = s(1)t(n) + s(2)t(n-1) + ... + s(k)t(n-k+1), where k = [ n/2 ], s = (Lucas numbers), t = A000201 (lower Wythoff sequence).at n=23A025094
• Let p1, p2 be first pair of consecutive primes with difference 2n; let p3, p4 be 2nd such pair; sequence gives "wadi" value p3-p1.at n=21A046728
• Values of n such that N=(an+1)(bn+1)(cn+1) is a 3-Carmichael number (A087788), where a,b,c = 1,2,33.at n=4A064253
• Numbers m such that N = (am+1)(bm+1)(cm+1) is a 3-Carmichael number (A087788), where a,b,c = 1,2,55.at n=4A065696
• Smallest triangular number which is a multiple (>1) of the n-th triangular number.at n=27A068084
• Triangular numbers with sum of digits = 15.at n=28A068130
• Triangular numbers of the form 21*k.at n=38A069499
• Triangular numbers whose digit permutations yield at least two further triangular numbers.at n=17A069674
• Numbers n such that sum of distinct primes dividing n is divisible by the largest prime dividing n. Also n is neither a prime, nor a true power of prime and n is squarefree. Squarefree solutions of A071140.at n=22A071141
• Numbers n such that sum of distinct primes dividing n is divisible by the largest prime dividing n. Also n has exactly 5 distinct prime factors and n is squarefree.at n=5A071144
• Squarefree numbers k such that the largest prime factor of k is equal to the sum of the other prime factors of k.at n=21A071312
• Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=6.at n=33A076672
• Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=7.at n=29A076673
• Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=10.at n=29A076675
• Smallest a(n)>a(n-1) such that a(n)^2+a(n-1)^2 is a perfect square, a(1)=11.at n=27A076676
• Sieve performed by successive iterations of steps where step m is: keep m terms, remove the next 4 and repeat; as m = 1,2,3,.. the remaining terms form this sequence.at n=13A112562
• Hexagonal numbers for which the sum of the digits is also a hexagonal number.at n=22A117062
• Hexagonal numbers for which both the sum of the digits and the product of the digits are also hexagonal numbers.at n=12A117064