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.
A081210 := proc(n) local a,pe; a :=1 ; for pe in ifactors(n)[2] do a := a*A070321(op(1,pe)^op(2,pe)) ; end do: a ; end proc: seq(A081210(n),n=1..100) ; # R. J. Mathar, May 25 2023
gsf[n_] := For[k = n, True, k--, If[ SquareFreeQ[k], Return[k]]]; a[n_] := Times @@ gsf /@ Power @@@ FactorInteger[n]; Table[a[n], {n, 1, 80}] (* Jean-François Alcover, Mar 27 2013 *)
a(n) = {my(f = factor(n)); prod(i = 1, #f~, if(f[i,2] == 1, f[i,1], my(k = f[i,1]^f[i,2]); while(!issquarefree(k), k--); k));} \\ Amiram Eldar, Jun 09 2025
gsf[n_] := For[k = n, True, k--, If[SquareFreeQ[k], Return[k]]]; A081210[n_] := Times @@ gsf /@ Power @@@ FactorInteger[n]; a[n_] := Module[{cnt = 0}, FixedPoint[(cnt++; A081210[#])&, n]; cnt-1]; Table[a[n], {n, 1, 105}] (* Jean-François Alcover, Mar 27 2013, updated Nov 27 2023 *)
Recall that A081210 = (in prime factorization of n: replace each prime power p^e = by the greatest squarefree number <= p^e). Consider n = 84 = 2*2*3*7, A081210(84) = 3*3*7 = 63, A081210(A081210(84)) = A081210(63) = 7*7 = 49 = a(84), A081210(A081210(A081210(84))) = A081210(A081210(63)) = A081210(49) = 47, A081212(49) = 3 as A081210(47) = 47 hence A081213(84) = 47, Therefore a(84) <> A081213(84), 49 <> 47.
A081211 := proc(n) A081210(A081210(n)) ; end proc: seq(A081211(n),n=1..84) ; # R. J. Mathar, May 25 2023
gsf[n_] := For[k = n, True, k--, If[SquareFreeQ[k], Return[k]]]; A081210[n_] := Times @@ gsf /@ Power @@@ FactorInteger[n]; a[n_] := A081210[A081210[n]]; Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Sep 12 2023 *)
A081210(n) = {my(f = factor(n)); prod(i = 1, #f~, if(f[i,2] == 1, f[i,1], my(k = f[i,1]^f[i,2]); while(!issquarefree(k), k--); k));} a(n) = A081210(A081210(n)); \\ Amiram Eldar, Jun 09 2025
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