A130849 a(n) is half the sum of the terms in the n-th antidiagonal of the table A130836.

0, 1, 1, 4, 2, 7, 4, 9, 8, 15, 6, 19, 13, 16, 13, 28, 15, 32, 17, 28, 27, 40, 16, 41, 34, 39, 30, 55, 28, 59, 34, 53, 50, 59, 32, 75, 57, 64, 41, 84, 47, 88, 55, 66, 72, 97, 42, 97, 71, 90, 70, 113, 65, 104, 67, 104, 97, 128, 56, 133, 103, 102, 82, 129, 89, 150, 99, 130, 100

Offset: 1

Author

Jacob Woolcutt (woolcutt(AT)gmail.com), Jul 21 2007

Keywords

• nonn
• easy

Examples

			d(3, 1) = 1
d(2, 2) = 0
d(1, 3) = 1
So a(3) = 1/2 * (1 + 0 + 1) = 1
		

Crossrefs

Equals half the antidiagonal sums of A130836.

Programs

Mathematica

MultDistance[m_, n_] := Module[{ mfac = FactorInteger[m], nfac = FactorInteger[ n]}, Plus @@ Map[(If[Length[ # ] == 1, #[[1, 2]], Abs[ #[[1, 2]] - #[[2, 2]]]]) &, Split[ Sort[Flatten[{mfac, nfac}, 1]], (#1[[1]] == #2[[1]]) &]]] DiagSum[n_] := 1/2 Sum[MultDistance[n - i, i + 1], {i, 0, n - 1}] Table[DiagSum[j], {j, 1, 1000}]

PARI

multDist(m, n) = {if (m==n, 0, my(f=vecsort(concat(factor(m)[, 1], factor(n)[, 1]),, 8)); sum(i=1, #f, abs(valuation(m, f[i])-valuation(n, f[i]))))};
a(n)={sum(i=0, (n-1)/2, multDist(n-i, i+1))}; \\ edited by Michel Marcus, Sep 20 2018

Formula

a(n) = 1/2 * Sum_{i=0..n-1} d(n-i, i+1) where, if m = Sum_{k} p_k^e^k, and n = Sum_{k} p_k^f^k, then d(m, n) = Sum_{i=1..k} abs(e_i - f_i), the multiplicative distance between m and n.

Extensions

Program and corrections by Charles R Greathouse IV, Sep 02 2009

Edited by Michel Marcus, Sep 20 2018