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 A239563 Numbers n such that there are a, b with abs(sigma(a) - sigma(b)) = sigma(n) - n and a U b = n, where U is decimal concatenation. 3

%I

%S 23,47,139,529,611,911,1109,1445,1621,2003,2521,2531,4007,4361,4879,

%T 7169,9011,9013,9481,13009,18883,22081,24257,25031,45349,49901,56081,

%U 90011,98941,99101,133705,160031,169181,200003,202289,210181,250031,307289,336961,357101

%N Numbers n such that there are a, b with abs(sigma(a) - sigma(b)) = sigma(n) - n and a U b = n, where U is decimal concatenation.

%H Paolo P. Lava and Giovanni Resta, <a href="/A239563/b239563.txt">Table of n, a(n) for n = 1..207</a>(terms < 3*10^9, first 50 terms from Paolo P. Lava)

%e For n = 9481 we can consider 9481 = 9 U 481 and sigma(9481) = 10000, sigma(481) = 532, sigma(9) = 13 and 532 - 13 = 519 = 10000 - 9481.

%p with(numtheory);

%p T:=proc(t) local w,x,y; x:=t; y:=0; while x>0 do x:=trunc(x/10); y:=y+1; od; end:

%p P:=proc(q) local a,b,c,d,i,n;

%p for n from 1 to q do a:=sigma(n); b:=T(n);

%p for i from 1 to b-1 do c:=trunc(n/10^i); d:=n-c*10^i;

%p if abs(sigma(c)-sigma(d))=a-n then print(n); break; fi;

%p od; od; end: P(10^9);

%Y Cf. A000203, A239562.

%K nonn,base

%O 1,1

%A _Paolo P. Lava_, Mar 21 2014

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Last modified December 7 23:32 EST 2022. Contains 358671 sequences. (Running on oeis4.)