login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A285079 Oblong numbers the product of whose digits are positive oblong numbers. 1
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 21 11:35 EDT 2019. Contains 328296 sequences. (Running on oeis4.)