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 A289507 The sum of squares of the elements of a finite multiset of positive integers divided by their gcd, the multiset {s_j} being indexed by n = Product_j p_{s_j}, where p_{s_j} is the s_j-th prime. 13
 0, 1, 2, 2, 3, 5, 4, 3, 4, 10, 5, 6, 6, 17, 13, 4, 7, 9, 8, 11, 10, 26, 9, 7, 6, 37, 6, 18, 10, 14, 11, 5, 29, 50, 25, 10, 12, 65, 20, 12, 13, 21, 14, 27, 17, 82, 15, 8, 8, 19, 53, 38, 16, 13, 34, 19, 34, 101, 17, 15, 18, 122, 12, 6, 15, 30, 19, 51 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Given an integer linear equation Sum_{j=1..k} e_j x_j = 0, a(n) is also the modulus of the determinant whose first row is e_1, e_2, ..., e_k and whose other k-1 rows form an integral basis for the integer solution space of the equation. Here n = Product_j p_{e_j}, where p_{e_j} is the e_j-th prime. For the proof, see Links. Also a(n) = A289506(n) when gcd_j e_j = 1, which occurs for the numbers n in A289509. LINKS Alois P. Heinz, Table of n, a(n) for n = 1..20000 Christopher J. Smyth, A determinant associated to an integer linear equation FORMULA a(n) = (Sum_j e_j^2)/gcd_j(e_j), where n = Product_j p_{e_j}. EXAMPLE For n = 63 = 3^2*7 = p_2*p_2*p_4, the corresponding multiset is {2,2,4}, and a(63) = (2^2 + 2^2 + 4^2)/2 = 12. Also the relevant determinant is Det([[2,2,4],[-1,1,0],[-2,0,1]]) = 12. MAPLE p:=1: for ind to 1000 do p:=nextprime(p); primeindex[p]:=ind; od: # so primeindex[p]:=k if p is the k-th prime out:=: for n from 2 to 100 do f:=ifactors(n); m:=[]; g:=0; for k to nops(f) do pow:=f[k]; ind:=primeindex[pow]; g:=gcd(g, ind); for e to pow do m:=[op(m), ind]; od; od; out:=[op(out), sum(m[jj]^2, jj=1..nops(m))/g]; od:print(out); # second Maple program: with(numtheory): a:= n-> (l-> add(i^2*i, i=l)/`if`(n=1, 1, igcd(seq(i,          i=l))))(map(i-> [pi(i), i], ifactors(n))): seq(a(n), n=1..80);  # Alois P. Heinz, Aug 05 2017 MATHEMATICA a[n_] := Module[{m}, m = Table[{p, e} = pe; Table[PrimePi[p], {e}], {pe, FactorInteger[n]}] // Flatten; (m.m)/GCD @@ m]; a = 0; Array[a, 80] (* Jean-François Alcover, May 05 2019 *) PROG (PARI) a(n) = if (n==1, 0, my(f=factor(n)); sum(k=1, #f~, f[k, 2]*primepi(f[k, 1])^2) /gcd(apply(x->primepi(x), f[, 1]))); \\ Michel Marcus, Jul 19 2017 CROSSREFS Cf. A289506, A289509. Cf. A056239, where the same encoding for integer multisets ('Heinz encoding') is used. Sequence in context: A299995 A113167 A036014 * A076228 A317050 A243970 Adjacent sequences:  A289504 A289505 A289506 * A289508 A289509 A289510 KEYWORD nonn,look AUTHOR Christopher J. Smyth, Jul 07 2017 STATUS approved

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Last modified January 26 23:05 EST 2020. Contains 331289 sequences. (Running on oeis4.)