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A300447
Numbers x such that sigma(x) = sigma(y), with x<>y, where y is the 10's complement mod 10 of the digits of x.
2
54, 56, 513, 520, 546, 564, 580, 597, 4845, 5130, 5223, 5454, 5656, 5887, 5970, 6265, 44226, 46365, 48450, 50260, 50840, 51300, 52230, 52520, 53768, 57342, 58580, 58870, 59700, 62650, 64745, 66884, 463650, 477972, 484500, 489132, 489632, 493752, 501536, 503274
OFFSET
1,1
LINKS
EXAMPLE
sigma(54) = sigma(56) = 120;
sigma(513) = sigma(597) = 800;
sigma(477972) = sigma(633138) = 1415232.
MAPLE
with(numtheory): P:=proc(q) local a, b, k, n;
for n from 1 to q do a:=convert(n, base, 10);
for k from 1 to nops(a) do a[k]:=(10-a[k]) mod 10; od; b:=0;
for k from 1 to nops(a) do b:=b*10+a[nops(a)-k+1]; od;
if b<>n and sigma(b)=sigma(n) then print(n); fi; od; end: P(10^6);
MATHEMATICA
Select[Range[10^6], Apply[And[#1 != #2, DivisorSigma[1, #1] == DivisorSigma[1, #2]] &, {#, FromDigits[IntegerDigits[#] /. d_?Positive :> 10 - d]}] &] (* Michael De Vlieger, Mar 09 2018 *)
PROG
(PARI) isok(x) = {my(dx = digits(x), dy = vector(#dx, k, (10-dx[k]) % 10), y = fromdigits(dy)); (x != y) && (sigma(x) == sigma(y)); } \\ Michel Marcus, Mar 07 2018
CROSSREFS
Sequence in context: A107936 A252722 A326181 * A344809 A344810 A295696
KEYWORD
nonn,base,easy
AUTHOR
Paolo P. Lava, Mar 06 2018
STATUS
approved