1,1

If we allow b=0 then the first solutions are N = 11110, 12120, 13130, ..., i.e., concat(10x+y, 10x+y,0) = concat(x, 10y+x, 10y) with x, y in {1, ..., 9}.

Hans Havermann, Table of n, a(n) for n = 1..2891 (terms 1..488 from M. F. Hasler)

Eric Angelini, 770700, SeqFan list, Feb. 13, 2016.

190319129 = 1903.1912.9 = 190.319.129, where "." denotes concatenation and the middle term is the sum of the first and last term, 1912 = 1903 + 9, 319 = 190 + 129.

191419228 = 1914.1922.8 = 191.419.228, etc.

There are 28 terms with 9 digits that are all of this type, which we call (4,4,1) & (3,3,3).

Then there are 208 terms with 11 digits, namely 64 of type (4,4,3) & (1,5,5), 72 of type (5,5,1) & (3,4,4), and 72 of type (5,5,1) & (4,4,3).

Then there are 252 terms with 12 digits, ranging from 18913.19012.99 = 1891.3190.1299 to 79799.79818.19 = 7979.9798.1819, all of this type (5,5,2) & (4,4,4).

(PARI) show(LCc)={TCc=10^LCc; for(Lb=1, LCc-1, Tb=10^Lb; for(Cc=TCc\10, TCc-1, for(b=Tb\10, Tb-1, Aa = Cc-b; Tc=1; Ta=10; while( Cc > Tc*=10, TC=TCc\Tc; Cc%Tc*10<Tc && next; cb = Cc%Tc * Tb + b; while(Aa\Ta+cb>(aC=Aa%Ta*TC +Cc\Tc) && Aa > Ta*=10, ); Aa>Ta || next(2); Aa\Ta+cb == aC && (Aa%Ta*10>Ta) && print1(Aa, Cc, b", ")))))}

for(L=1, 5, show(L)) \\ Yields results only from n=4 on. WARNING, beyond the 29th term the list is no longer in order, some terms with LCc=5 are smaller than other terms with LCc=4.

Sequence in context: A178565 A195902 A181321 * A209597 A251514 A268844

Adjacent sequences: A267767 A267768 A267769 * A267771 A267772 A267773

nonn,base

Eric Angelini, Hans Havermann and M. F. Hasler, Feb 14 2016

approved