

A300891


Lefttruncatable nonzero triangular numbers.


0



1, 3, 6, 21, 36, 66, 91, 136, 406, 666, 703, 903, 3003, 6903, 7021, 8001, 5000703
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

Leading zeros in postfix strings are ignored (e.g., 003 and 03 are both equivalent to 3). Zero was excluded from the set because otherwise any integer starting with 1, 3, or 6 followed by any number of zeros would be a member.
Compare this sequence with the righttruncatable triangular numbers listed in A202269.
Conjecture: this sequence appears to be finite and full (bruteforce tested up to 228*10^9 digits).


LINKS



EXAMPLE

6903 is a term because it is a nonzero triangular number, and 903 is a term of the sequence.


MAPLE

isA300891 := proc(n)
option remember ;
if n in {1, 3, 6} then
return true;
elif n < 10 then
return false;
end if;
if isA000217(n) then
dgs := max(1, ilog10(n)+1) ;
return procname( modp(n, 10^(dgs1))) ;
else
return false;
end if;
end proc:
for i from 1 do
if isA300891(t) then
print(t) ;
end if;


CROSSREFS



KEYWORD

nonn,base,more


AUTHOR



STATUS

approved



