

A300891


Lefttruncatable nonzero triangular numbers.


0



1, 3, 6, 21, 36, 66, 91, 136, 406, 666, 703, 903, 3003, 6903, 7021, 8001, 5000703
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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

Table of n, a(n) for n=1..17.


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
t := A000217(i) ;
if isA300891(t) then
print(t) ;
end if;
end do: # R. J. Mathar, May 02 2018


CROSSREFS

Cf. A000217, A202269.
Sequence in context: A174461 A050611 A270510 * A056499 A056489 A015649
Adjacent sequences: A300888 A300889 A300890 * A300892 A300893 A300894


KEYWORD

nonn,base,more


AUTHOR

Stanislav Sykora, Mar 14 2018


STATUS

approved



