A285079 Oblong numbers the product of whose digits are positive oblong numbers.

2, 6, 12, 56, 132, 156, 756, 2756, 4556, 6162, 6972, 7656, 13572, 21756, 31152, 33672, 45156, 61752, 84972, 153272, 166872, 279312, 467172, 626472, 661782, 1273512, 1412532, 1541322, 1568756, 1596432, 1786232, 1867322, 2678132, 2817362, 3416952, 3521252

Offset

1,1

Comments

Oblong numbers are numbers of the form k*(k+1) (A002378).

Links

Robert Israel and Giovanni Resta, Table of n, a(n) for n = 1..391 (terms < 10^25, first 221 terms from Robert Israel)

Maple

filter:= proc(x) local t; t:= convert(convert(x, base, 10), `*`);
t > 0 and issqr(1+4*t); end proc:
select(filter, [seq(x*(1+x), x=1..10^4)]); # Robert Israel, Apr 14 2017

Mathematica

f[x_] := Sqrt[1 + 4 (Times @@ IntegerDigits[x])]; Select[Table[n (n + 1), {n, 1, 10000}], f[#] > 1 && Mod[f[#], 2] == 1 &]

Crossrefs

Cf. A002378, A053059, A069077.

Sequence in context: A152873 A175810 A083001 * A119862 A111936 A232090

Adjacent sequences: A285076 A285077 A285078 * A285080 A285081 A285082

Keyword

nonn,base

Author

Melvin Peralta, Apr 09 2017

Status

approved