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 A385209 #22 Jun 30 2025 07:43:23 %S A385209 1,2,3,4,9,6,15,16,81,12,45,64,729,24,105,36,225,48,405,1024,59049,60, %T A385209 315,4096,531441,192,3645,144,2025,120,945,65536,43046721,180,1575, %U A385209 262144,387420489,240,2835,576,18225,3072,295245,4194304,31381059609,360,3465,1296 %N A385209 Least k such that A086369(k) = n. %C A385209 A086369(n) is also the cardinality of the set containing the divisors d of n and those 0 < m < n satisfying m + d = n. %F A385209 a(2*p-1) = 3^(p-1) for prime p. - _Jinyuan Wang_, Jun 30 2025 %e A385209 a(4) = 4 since 4 is the least k such that A086369(k) = 4. %e A385209 a(13) = 729 since 729 is the least k such that A086369(k) = 13. %o A385209 (PARI) a(n,k) = my(f); (f(n) = if(n%2==1, 1+2*sumdiv(n,d,d<n/2), 2+2*sumdiv(n,d,d<n/2))); for(m=1, k, if(f(m)==n, return(m), 0)) \\ k defines the length of the search, returns 0 if n is not found %Y A385209 Cf. A086369, A385202. %K A385209 nonn %O A385209 1,2 %A A385209 _Miles Englezou_, Jun 21 2025 %E A385209 a(45)-a(48) from _Jinyuan Wang_, Jun 30 2025