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A285079 Oblong numbers the product of whose digits are positive oblong numbers. 1

%I

%S 2,6,12,56,132,156,756,2756,4556,6162,6972,7656,13572,21756,31152,

%T 33672,45156,61752,84972,153272,166872,279312,467172,626472,661782,

%U 1273512,1412532,1541322,1568756,1596432,1786232,1867322,2678132,2817362,3416952,3521252

%N Oblong numbers the product of whose digits are positive oblong numbers.

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

%H Robert Israel and Giovanni Resta, <a href="/A285079/b285079.txt">Table of n, a(n) for n = 1..391</a> (terms < 10^25, first 221 terms from Robert Israel)

%p filter:= proc(x) local t; t:= convert(convert(x,base,10),`*`);

%p t > 0 and issqr(1+4*t); end proc:

%p select(filter, [seq(x*(1+x),x=1..10^4)]); # _Robert Israel_, Apr 14 2017

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

%Y Cf. A002378, A053059, A069077.

%K nonn,base

%O 1,1

%A _Melvin Peralta_, Apr 09 2017

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Last modified November 18 01:41 EST 2019. Contains 329242 sequences. (Running on oeis4.)