OFFSET
1,2
COMMENTS
a(12) > 10^12, if it exists. - Amiram Eldar, Oct 11 2024
FORMULA
Solutions to c(x^2) = y^2, values of x^2; where c(j) is the j-th composite number; see program.
EXAMPLE
a(4) = 1024 = 32^2 corresponds to the composite number 1225 = 35^2.
MATHEMATICA
c[x_] := FixedPoint[x+PrimePi[ # ]+1&, x]; Do[s=c[n^2]; If[IntegerQ[Sqrt[s]], Print[n^2]], {n, 1, 1000000}]
PROG
(PARI) lista(cmax) = {my(k = 0); forcomposite(c = 1, , k++; if(issquare(k) && issquare(c), print1(k, ", "))); } \\ Amiram Eldar, Oct 11 2024
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Labos Elemer, Jul 19 2002
EXTENSIONS
a(9)-a(11) from Donovan Johnson, Jan 24 2011
STATUS
approved