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Digit sum of composite odd number equals digit sum of juxtaposition of its prime factors (counted with multiplicity).
2

%I #18 Aug 25 2024 17:03:41

%S 27,85,121,265,319,355,391,483,517,535,627,645,663,729,825,861,895,

%T 913,915,985,1111,1165,1219,1255,1449,1507,1581,1633,1755,1795,1881,

%U 1903,1921,1935,2067,2079,2155,2173,2227,2265,2373,2409,2461,2475,2515,2583

%N Digit sum of composite odd number equals digit sum of juxtaposition of its prime factors (counted with multiplicity).

%C Odd Smith numbers. - _Robert Israel_, Aug 25 2024

%H Robert Israel, <a href="/A036925/b036925.txt">Table of n, a(n) for n = 1..10000</a>

%p filter:= proc(n) local F;

%p if isprime(n) then return false fi;

%p F:= ifactors(n)[2];

%p convert(convert(n, base, 10), `+`) = convert(map(t -> t[2]*convert(convert(t[1], base, 10), `+`), F), `+`)

%p end proc:

%p select(filter, [seq(i,i=9..10000,2)]); # _Robert Israel_, Aug 25 2024

%Y Cf. A006753, A019506, A036924.

%K nonn,base

%O 1,1

%A _Patrick De Geest_, Jan 04 1999

%E Title made more precise by _Sean A. Irvine_, Nov 30 2020