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A239724 Composite numbers n such that if n = a U b (where U denotes concatenation) then a’ + b’ = n’, where a’, b’ and n’ are the arithmetic derivatives of a, b and n. 1
169, 209, 1027, 1219, 1339, 1929, 1966, 2581, 11569, 17251, 17845, 18419, 26093, 59987, 98699, 106159, 107629, 115069, 131179, 137533, 147019, 150071, 151519, 155471, 168505, 186911, 188297, 207413, 217999, 221027, 230183, 231437, 276413, 298891, 368813, 400921 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..100

EXAMPLE

The arithmetic derivative of 2581 is 118. Consider 2581 = 25 U 81. The arithmetic derivative of 25 is 10 and of 81 is 108. Therefore we have 10 + 108 = 118.

MAPLE

with(numtheory); 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:=proc(q) local a, b, c, d, f, g, i, n, p; for n from 1 to q do if not isprime(n) then b:=T(n);

a:=n*add(op(2, p)/op(1, p), p=ifactors(n)[2]); for i from 1 to b-1 do c:=trunc(n/10^i); d:=n-c*10^i;

f:=c*add(op(2, p)/op(1, p), p=ifactors(c)[2]); g:=d*add(op(2, p)/op(1, p), p=ifactors(d)[2]);

if f+g=a then print(n); break; fi; od; fi; od; end: P(10^9);

CROSSREFS

Cf. A003415.

Sequence in context: A044869 A260055 A235718 * A038512 A141075 A124979

Adjacent sequences:  A239721 A239722 A239723 * A239725 A239726 A239727

KEYWORD

nonn,base

AUTHOR

Paolo P. Lava, Mar 25 2014

STATUS

approved

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Last modified June 16 09:48 EDT 2021. Contains 345056 sequences. (Running on oeis4.)