OFFSET
1,2
LINKS
Christian N. K. Anderson, Table of n, a(n) for n = 1..500
Christian N. K. Anderson, Decomposition of a(n) into its square root, and truncated cube root for n=0..500.
FORMULA
For n > 11: a(n)=(100*(n-6)^3)^2 (188210961 is the last "exception" as is easy to prove with the help of the Nagell-Lutz theorem). - Reiner Moewald, Dec 30 2013
EXAMPLE
188210961=13719^2, while 18821096=266^3.
MATHEMATICA
cQ[n_]:=IntegerQ[Surd[FromDigits[Most[IntegerDigits[n]]], 3]]; Select[Range[ 700000]^2, cQ] (* Harvey P. Dale, Feb 21 2014 *)
PROG
(R) trimR=function(x) { x=as.character(x); ifelse(nchar(x)<2, 0, substr(x, 1, nchar(x)-1)) }
iscube<-function(x) ifelse(as.bigz(x)<2, T, all(table(as.numeric(factorize(x)))%%3==0))
which(sapply(1:6400, function(x) iscube(trimR(x^2))))^2
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Christian N. K. Anderson and Kevin L. Schwartz, Jun 04 2013
STATUS
approved