21691

Appears in sequences

• Strong pseudoprimes to base 93.at n=20A020319
• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 35 ones.at n=4A031803
• a(n) is the smallest m such that the elliptic curve x^3 + y^3 = m has rank n, or -1 if no such m exists.at n=4A060748
• Numbers k such that sopf(k) = sopf(k^2 - 1), where sopf(k) = A008472(k).at n=11A064019
• Numbers k for which 16*k+1, 16*k+3, 16*k+7, 16*k+13 and 16*k+15 are primes.at n=3A123990
• Expansion of 1/(1 - x^2 - x^7 - x^12 + x^14) (a Salem polynomial).at n=61A143619
• Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, 0, 1), (-1, 1, 0), (0, -1, 1), (1, 0, 0), (1, 1, -1)}.at n=9A148738
• Totally multiplicative sequence with a(p) = a(p-1) + 9 for prime p.at n=34A166706
• Sequence defined by the recurrence formula a(n+1)=sum(a(p)*a(n-p)+k,p=0..n)+l for n>=1, with here a(0)=1, a(1)=5, k=0 and l=-1.at n=7A176751
• a(0) = 1; for n > 0, a(n) = 41*n^2 + 2.at n=23A206399
• Composite numbers for which the root mean square of proper divisors is an integer.at n=25A247135
• Weak Goodstein numbers: a(n) = g_n(n), where g_n(n) is the weak Goodstein function.at n=17A266202
• a(n) = G_n(5), where G_n(k) is the Goodstein function defined in A266201.at n=17A266204
• Numbers k such that k![10]-2 is prime, where k![10] is the ten-fold multifactorial.at n=61A283559
• Number of nX4 0..1 arrays with every element unequal to 1, 2, 3, 5 or 8 king-move adjacent elements, with upper left element zero.at n=6A305363
• Number of nX7 0..1 arrays with every element unequal to 1, 2, 3, 5 or 8 king-move adjacent elements, with upper left element zero.at n=3A305366
• T(n,k)=Number of nXk 0..1 arrays with every element unequal to 1, 2, 3, 5 or 8 king-move adjacent elements, with upper left element zero.at n=48A305367
• T(n,k)=Number of nXk 0..1 arrays with every element unequal to 1, 2, 3, 5 or 8 king-move adjacent elements, with upper left element zero.at n=51A305367
• Numbers k for which rank of the elliptic curve y^2 = x^3 - 432*k^2 is 4.at n=0A309964