20405

Appears in sequences

• Dirichlet convolution of b_n=2^(n-1) with c_n=3^(n-1).at n=9A034735
• A diagonal of A008296.at n=19A059302
• Numbers k such that phi(5k-1) = sigma(k).at n=1A067224
• Multiples of 11 with digit sum 11, with no zero digits in odd places.at n=20A083512
• Consider recurrence b(0) = (2n+1)/2, b(n) = b(0)*floor(b(n-1)); sequence gives first integer reached.at n=25A087675
• Moebius transform of binomial(n+3, 4).at n=24A117109
• Numbers k such that k and k+1 have 4 distinct prime factors.at n=29A140078
• Coefficients in the expansion of C/B^2, in Watson's notation of page 106.at n=20A160461
• Numbers n having at least two distinct symmetrical pairs of divisors (a, b) and (b', a') such that n = a*b = b'*a' with a' = reverse(a) and b' = reverse(b).at n=33A228164
• Number of partitions of n such that (number of distinct parts) = maximal multiplicity of the parts.at n=50A239964
• Numbers k such that (64*10^k + 287)/9 is prime.at n=27A272195
• Numbers with digit sum 11 that are multiples of 11.at n=29A283742
• a(n) is the smallest number such that there are exactly n numbers k (including a(n) itself) such that U(k) is isomorphic to U(a(n)) (or 0 if no such number exists). Here U(k) is the multiplicative group of integers modulo k.at n=33A303712
• Numbers k such that k and k+1 are the product of exactly four distinct primes.at n=13A318896
• Numbers k such that k and k+1 each have at least 4 distinct prime factors.at n=29A321504
• Numbers k such that k + A067666(k) is a square.at n=29A386257