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%I #23 Mar 11 2021 02:10:08
%S 6,55,474,9360,80029,355452,684228,512562258,986657022,4382255359,
%T 37466984190,739114421304,6319209189385,54027365220036,
%U 9112295268838531,40472427468293976,77907423180308442,346027256676968725,58361212342395772530,498971064164650006699,4266054677084570952198
%N Integers y corresponding to the terms of A342387.
%H Chai Wah Wu, <a href="/A342388/b342388.txt">Table of n, a(n) for n = 1..950</a>
%H Josep M. Brunat and Joan-Carles Lario, <a href="https://arxiv.org/abs/2103.05306">A problem on concatenated integers</a>, arXiv:2103.05306 [math.NT], 2021.
%e y=6 is a term with x=20 because 7/21 = 207/621.
%o (PARI) isok(x) = {for (y=1, x-1, if ((y+1)/(x+1) == eval(Str(x, y+1))/eval(Str(y, x+1)), return (y)); ); } \\ A342387
%o for (x=1, 10000, if (y=isok(x), print1(y, ", ")))
%o (Python)
%o A342388_list, x, s1, s2, m = [], 1, '1', '2', 10
%o while x < 10**6:
%o for y in range(1,x):
%o if (x+1)*int(s1+str(y+1)) == (y+1)*(y*m+x+1):
%o A342388_list.append(y)
%o break
%o x += 1
%o s1, s2 = s2, str(x+1)
%o m = 10**(len(s2)) # _Chai Wah Wu_, Mar 10 2021
%o (Python)
%o # based on formula in Brunat and Lario 2021
%o xlist, ylist, A342388_list, x, y = [4,20,39], [1,6,12], [6], 39, 12
%o while len(A342388_list) < 100:
%o if len(str(x+1)) == len(str(y+1))+1:
%o A342388_list.append(y)
%o x, y = 19*xlist[-3]+60*ylist[-3]+39, 6*xlist[-3]+19*ylist[-3]+12
%o xlist, ylist = xlist[1:] + [x], ylist[1:] + [y] # _Chai Wah Wu_, Mar 10 2021
%Y Cf. A342387.
%K nonn,base
%O 1,1
%A _Michel Marcus_, Mar 10 2021
%E More terms from _Chai Wah Wu_, Mar 10 2021
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