20534

Appears in sequences

• Consider a number of k digits n = d_(k)*10^(k-1) + d_(k-1)*10^(k-2) + … + d_(2)*10 + d_(1). Sequence lists the numbers n such that Sum_{i=1..k-1}{phi(Sum_{j=1..i}{d_(j)*10^(j-1)})} = Sum_{i=1..k-1}{sigma(Sum_{j=1..i}{d_(k-j+1)*10^(i-j)})} (see example below).at n=19A244069
• Least number k such that k^n + k +/- 1 are twin primes, or 0 if no such k exists.at n=45A248081
• a(n) is the number of terms in the analog of A121805 but starting with n, or -1 if that sequence is infinite.at n=12A330128
• Upper (1/2,1/3) midsequence of (n^2) and (n^3); see Comments.at n=39A389583