OFFSET
1,3
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..130
EXAMPLE
766459 is in the sequence because it is a heptagonal number and the product of its digits (45360) is also a heptagonal number
MAPLE
a:=proc(n) local hn, hnn: hn:=convert(n*(5*n-3)/2, base, 10): hnn:=product(hn[j], j=1..nops(hn)): if type((3+sqrt(9+40*hnn))/10, integer)=true then n*(5*n-3)/2 else fi end: seq(a(n), n=0..10000); # Emeric Deutsch, Apr 16 2006
MATHEMATICA
Join[{0}, Select[LinearRecurrence[{3, -3, 1}, {0, 1, 7}, 7000], IntegerQ[(3+ Sqrt[ 40*Times@@IntegerDigits[#]+9])/10]&]] (* Harvey P. Dale, Jun 17 2015 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Luc Stevens (lms022(AT)yahoo.com), Apr 11 2006
EXTENSIONS
More terms from Emeric Deutsch, Apr 16 2006
STATUS
approved