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A050219 Smaller of Smith brothers. 6
728, 2964, 3864, 4959, 5935, 6187, 9386, 9633, 11695, 13764, 16536, 16591, 20784, 25428, 28808, 29623, 32696, 33632, 35805, 39585, 43736, 44733, 49027, 55344, 56336, 57663, 58305, 62634, 65912, 65974, 66650, 67067, 67728, 69279, 69835 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..1000

Eric Weisstein's World of Mathematics, Smith Brothers.

MAPLE

issmith:= proc(n)

  if isprime(n) then return false fi;

  convert(convert(n, base, 10), `+`) = add(t[2]*convert(convert(t[1], base, 10), `+`), t=ifactors(n)[2])

end proc:

S:= select(issmith, {$4..10^5}):

sort(convert(S intersect map(`-`, S, 1), list)); # Robert Israel, Jan 15 2018

MATHEMATICA

smithQ[n_] := !PrimeQ[n] && Total[Flatten[IntegerDigits[Table[#[[1]], {#[[2]]}]& /@ FactorInteger[n]]]] == Total[IntegerDigits[n]];

Select[Range[10^5], smithQ[#] && smithQ[#+1]&] (* Jean-Fran├žois Alcover, Jun 07 2020 *)

PROG

(PARI) isone(n) = {if (!isprime(n), f = factor(n); sumdigits(n) == sum(k=1, #f~, f[k, 2]*sumdigits(f[k, 1])); ); }

isok(n) =  isone(n) && isone(n+1); \\ Michel Marcus, Jul 17 2015

CROSSREFS

Cf. A006753, A050220.

Sequence in context: A158395 A184077 A234652 * A051383 A293650 A233962

Adjacent sequences:  A050216 A050217 A050218 * A050220 A050221 A050222

KEYWORD

nonn,base

AUTHOR

Eric W. Weisstein

EXTENSIONS

Offset corrected by Arkadiusz Wesolowski, May 08 2012

STATUS

approved

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Last modified August 6 15:15 EDT 2020. Contains 336248 sequences. (Running on oeis4.)