This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A106317 #15 Feb 21 2025 11:48:48
%S A106317 1,2,3,5,7,11,13,17,19,21,23,29,31,37,41,43,47,53,59,61,67,71,73,79,
%T A106317 83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,
%U A106317 179,181,191,193,197,199
%N A106317 Numbers k such that the remainder of the harmonic residue of k when divided by k is k-1.
%F A106317 It appears that k is in the sequence iff k is prime or k is in {1, 21, 822857} (Verified to 3.1*10^6). It is true that if k is the product of two distinct primes, then k=21. - George J. Schaeffer (gschaeff(AT)andrew.cmu.edu), Apr 30 2005, _R. J. Mathar_, Jan 25 2017
%F A106317 There are no other nonprime terms below 10^11. - _Amiram Eldar_, Jan 09 2024
%o A106317 (PARI) is(n) = {my(f = factor(n)); n*numdiv(f) % sigma(f) == n - 1;} \\ _Amiram Eldar_, Jan 09 2024
%Y A106317 Cf. A106315, A106316.
%K A106317 nonn
%O A106317 1,2
%A A106317 George J. Schaeffer (gschaeff(AT)andrew.cmu.edu), Apr 29 2005