19547

Appears in sequences

• Composite numbers whose prime factors contain no digits other than 1 and 7.at n=41A036307
• Expansion of (1 - 4*x^2 - 8*x^3)/((1 + 2*x + 4*x^2)*(1 - x - 2*x - 4*x^2 - 4*x^3 + 16*x^4)).at n=8A129443
• This sequence and A139143 are complements. a(1) = 1, A139143(1) = 2, a(n+1) = a(n) + Sum_{k = 1..n} A139143(k).at n=45A139142
• Smallest k such that 34^k mod k = n.at n=23A178195
• G.f. satisfies: A(x) = 1 + Sum_{n>=1} x^n*A(x)^sigma(n), where sigma(n) = A000203(n) is the sum of divisors of n.at n=9A192497
• Numbers in A231626 but not in A343302; first of 5 consecutive deficient numbers in arithmetic progression with common difference > 1.at n=34A343303