login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

n times n+1 gives the concatenation of two numbers m and m+2.
5

%I #5 Aug 20 2019 11:18:23

%S 768,859,911,3286,6714,45453,54547,990101,8181820,70588234,343130555,

%T 362637364,363636362,420053632,421052633,497975710,502024290,

%U 578947367,579946368,636363638,637362636,656869445,706766919

%N n times n+1 gives the concatenation of two numbers m and m+2.

%H Robert Israel, <a href="/A116301/b116301.txt">Table of n, a(n) for n = 1..9000</a>

%p As:= {}:

%p for m from 2 to 20 do

%p acands:= map(t -> rhs(op(t)), [msolve(a*(a+1)=2, 10^m+1)]);

%p bcands:= map(t -> t*(t+1) mod 10^m, acands);

%p good:= select(t -> bcands[t]>=10^(m-1), [$1..nops(acands)]);

%p As:= As union convert(acands[good],set);

%p od:

%p sort(convert(As,list)); # _Robert Israel_, Aug 20 2019

%Y Cf. A116170, A116294, A116302, A116307.

%K nonn,base

%O 1,1

%A _Giovanni Resta_, Feb 06 2006