OFFSET
1,1
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
n=6 has 4 divisors. a(6) is not 12 or 18 because 12 and 18 have only 6 divisors as opposed to the 8 divisors required by the definition.
MAPLE
A129902 := proc(n) local m; m := 2 ; while numtheory[tau](m*n)<> 2*numtheory[tau](n) do m := m+1 ; od ; RETURN(m*n) ; end: for n from 1 to 100 do printf("%d, ", A129902(n)) ; od ; # R. J. Mathar, Jun 07 2007
MATHEMATICA
a[n_] := Module[{}, in = 2; While[Length[Divisors[in*n]] != 2*Length[Divisors[n]], in++ ]; in*n]; Table[a[i], {i, 1, 70}] (* Stefan Steinerberger, Jun 07 2007 *)
PROG
(PARI) a(n) = {my(k=1); while (numdiv(n*k) != 2*numdiv(n), k++); n*k; } \\ Michel Marcus, Sep 15 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
J. Lowell, Jun 04 2007
EXTENSIONS
STATUS
approved