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 A287958 #12 Jun 04 2017 16:39:08 %S A287958 1,2,2,3,2,3,4,6,6,4,5,4,3,4,5,6,10,12,12,10,6,7,6,15,4,15,6,7,8,14,6, %T A287958 20,20,6,14,8,9,8,21,12,5,12,21,8,9,10,18,24,28,30,30,28,24,18,10,11, %U A287958 10,9,64,35,6,35,64,9,10,11,12,22,30,36,40,42,42,40 %N A287958 Table read by antidiagonals: T(n, k) = least recursive multiple of n and k; n > 0 and k > 0. %C A287958 We say that m is a recursive multiple of d iff d is a recursive divisor of m (as described in A282446). %C A287958 More informally, the prime tower factorization of T(n, k) is the union of the prime tower factorizations of n and k (the prime tower factorization of a number is defined in A182318). %C A287958 This sequence has connections with the classical LCM (A003990). %C A287958 For any i > 0, j > 0 and k > 0: %C A287958 - A007947(T(i, j)) = A007947(lcm(i, j)), %C A287958 - T(i, j) >= 1, %C A287958 - T(i, j) >= max(i, j), %C A287958 - T(i, j) >= lcm(i, j), %C A287958 - T(i, 1) = i, %C A287958 - T(i, i) = i, %C A287958 - T(i, j) = T(j, i) (the sequence is commutative), %C A287958 - T(i, T(j, k)) = T(T(i, j), k) (the sequence is associative), %C A287958 - T(i, i*j) >= i*j, %C A287958 - if gcd(i, j) = 1 then T(i, j) = i*j. %C A287958 See also A287957 for the GCD equivalent. %H A287958 Rémy Sigrist, <a href="/A287958/b287958.txt">First 100 antidiagonals of array, flattened</a> %H A287958 Rémy Sigrist, <a href="/A287958/a287958.pdf">Illustration of the first terms</a> %e A287958 Table starts: %e A287958 n\k| 1 2 3 4 5 6 7 8 9 10 %e A287958 ---+----------------------------------------------- %e A287958 1 | 1 2 3 4 5 6 7 8 9 10 ... %e A287958 2 | 2 2 6 4 10 6 14 8 18 10 ... %e A287958 3 | 3 6 3 12 15 6 21 24 9 30 ... %e A287958 4 | 4 4 12 4 20 12 28 64 36 20 ... %e A287958 5 | 5 10 15 20 5 30 35 40 45 10 ... %e A287958 6 | 6 6 6 12 30 6 42 24 18 30 ... %e A287958 7 | 7 14 21 28 35 42 7 56 63 70 ... %e A287958 8 | 8 8 24 64 40 24 56 8 72 40 ... %e A287958 9 | 9 18 9 36 45 18 63 72 9 90 ... %e A287958 10 | 10 10 30 20 10 30 70 40 90 10 ... %e A287958 ... %e A287958 T(4, 8) = T(2^2, 2^3) = 2^(2*3) = 2^6 = 64. %o A287958 (PARI) T(n,k) = if (n*k==0, return (max(n,k))); my (g=factor(lcm(n,k))); return (prod(i=1, #g~, g[i,1]^T(valuation(n, g[i,1]), valuation(k, g[i,1])))) %Y A287958 Cf. A003990, A007947, A182318, A282446, A287957. %K A287958 nonn,tabl %O A287958 1,2 %A A287958 _Rémy Sigrist_, Jun 03 2017