21521

Properties

Appears in sequences

• Primes that remain prime through 2 iterations of function f(x) = 8x + 1.at n=40A023260
• Primes that remain prime through 3 iterations of function f(x) = 5x + 4.at n=31A023284
• Primes that remain prime through 3 iterations of function f(x) = 8x + 3.at n=7A023292
• Primes p whose reciprocal has period (p-1)/10.at n=29A056215
• Define C(n) by the recursion C(0) = 4*i where i^2 = -1, C(n+1) = 1/(1 + C(n)), then a(n) = 4*(-1)^n/Im(C(n)) where Im(z) denotes the imaginary part of z.at n=9A069961
• Primes which can be expressed as sum of distinct powers of 4.at n=29A077718
• Diagonal of triangle in A082737.at n=41A082738
• Primes arising in A090513.at n=4A090514
• Decimal Goedelization of antitheorems from propositional calculus, in Richard C. Schroeppel's metatheory of A101273.at n=16A100200
• Primes congruent to 49 mod 61.at n=35A142847
• Primes of the form XYX, where Y is a single digit.at n=30A154270
• Lesser of twin primes p1 such that p1*p2-4 and p1*p2-6 are twin prime numbers.at n=14A174957
• Primes of the form abcabc..abcab.at n=15A228627
• Primes whose base-4 representation also is the base 2-representation of a prime.at n=18A235461
• Initial members of prime quadruples (n, n+2, n+36, n+38).at n=20A248367
• Primes of the form k!6+16, where k!6 is the sextuple factorial number (A085158).at n=8A288613
• Number of connected undirected unlabeled loopless multigraphs with 4 vertices and n edges.at n=33A290778
• Number of fully chiral set-systems on n vertices.at n=4A330282
• Prime numbers whose binary expansion involves powers of 2 with only composite (or zero) exponents.at n=24A342481
• a(n) is the least number that reaches 1 after n iterations of the infinitary totient function A064380.at n=34A362025