25681

Appears in sequences

• G.f.: 1/Product_{k>=1} (1-prime(k)*x^prime(k)).at n=21A002098
• Strong pseudoprimes to base 20.at n=12A020246
• Strong pseudoprimes to base 29.at n=16A020255
• Strong pseudoprimes to base 92.at n=30A020318
• Numbers k such that the continued fraction for sqrt(k) has period 87.at n=18A020426
• Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 35.at n=1A031623
• Numerators of continued fraction convergents to sqrt(281).at n=7A041528
• Numerators of b(n) = (1/16^n)*(4/(8*n+1) - 2/(8*n+4) - 1/(8*n+5) - 1/(8*n+6)).at n=14A048581
• Numbers n such that h(n) = 3 h(n-1) where h(n) is the length of the sequence {n, f(n), f(f(n)), ...., 1} in the Collatz (or 3x + 1) problem. (The earliest "1" is meant.)at n=27A078420
• Semiprimes in A054567.at n=25A113692
• Composite numbers k that divide 3^k - 2^k - 1, excluding powers of 2, 3 and 7.at n=35A127073
• a(n) = 16*n^2 + 2*n + 1.at n=40A204675
• Composite numbers coprime to 6 such that A179382(n) = A000265(n-1), the odd part of n-1.at n=41A225913
• Numbers n such that the decimal number concat(6,n) is a square.at n=35A273361
• a(n) is the numerator of (120*n^2 + 151*n + 47)/(512*n^4 + 1024*n^3 + 712*n^2 + 194*n + 15).at n=14A374580