A036925 Digit sum of composite odd number equals digit sum of juxtaposition of its prime factors (counted with multiplicity).

27, 85, 121, 265, 319, 355, 391, 483, 517, 535, 627, 645, 663, 729, 825, 861, 895, 913, 915, 985, 1111, 1165, 1219, 1255, 1449, 1507, 1581, 1633, 1755, 1795, 1881, 1903, 1921, 1935, 2067, 2079, 2155, 2173, 2227, 2265, 2373, 2409, 2461, 2475, 2515, 2583

Offset: 1

Author

Patrick De Geest, Jan 04 1999

Keywords

• nonn
• base

Comments

Odd Smith numbers. - Robert Israel, Aug 25 2024

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006753, A019506, A036924.

Programs

Maple

filter:= proc(n) local F;
  if isprime(n) then return false fi;
  F:= ifactors(n)[2];
  convert(convert(n, base, 10), `+`) = convert(map(t -> t[2]*convert(convert(t[1], base, 10), `+`), F), `+`)
end proc:
select(filter, [seq(i,i=9..10000,2)]); # Robert Israel, Aug 25 2024

Extensions

Title made more precise by Sean A. Irvine, Nov 30 2020