A172509 Numbers n such that Omega(n) = Omega(n - (digital sum of n)).

1, 10, 14, 15, 20, 27, 28, 30, 40, 50, 52, 60, 70, 75, 76, 78, 80, 90, 102, 105, 112, 124, 125, 132, 135, 136, 140, 164, 165, 176, 182, 186, 188, 204, 212, 224, 232, 234, 248, 252, 264, 273, 275, 279, 280, 290, 292, 306, 308, 315, 328, 336, 343

Offset

1,2

Comments

Omega(n) is the number of prime divisors of n, A001222 (for n>0), taking Omega(0)=0.

Omega(a(n)) >= 3 for n >= 5. - Robert Israel, Jul 04 2019

Links

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

Example

a(1)=1 because Omega(1) = Omega(1 - (digital sum of 1)) = Omega(0) = 0;
a(2)=10 because Omega(10) = Omega(10 - (digital sum of 10)) = Omega(9) = 2.

Maple

filter:= proc(n) uses numtheory:
    bigomega(n) = bigomega(n - convert(convert(n, base, 10), `+`))
end proc:
select(filter, [$1..500]); # Robert Israel, Jul 04 2019

Mathematica

Join[{1}, Select[Range[2, 400], PrimeOmega[#]==PrimeOmega[#-Total[ IntegerDigits[ #]]]&]] (* Harvey P. Dale, Jun 21 2021 *)

Crossrefs

Cf. A001222.

Sequence in context: A209800 A119613 A154371 * A036338 A108793 A100929

Adjacent sequences: A172506 A172507 A172508 * A172510 A172511 A172512

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Nov 21 2010

Extensions

Corrected and edited by D. S. McNeil, Nov 21 2010

Status

approved