A050690 Sum of digits of zero-absent composite a(n) equals number of prime factors.

12, 32, 1152, 11232, 13122, 14112, 21312, 111132, 112112, 3121152, 11231232, 11354112, 812122112, 1251213312, 2211121152, 2211213312, 5121114112, 26122125312, 56321114112, 62214111232, 431711322112, 3421411213312, 11111212122112, 11112113242112

Offset

1,1

Comments

10^11 < a(21) <= 431711322112. a(22) <= 3421411213312. - Donovan Johnson, May 30 2010

Do all terms end in 2, i.e., is each term = 2 mod 10? (* Harvey P. Dale, May 26 2024 *)

Links

Table of n, a(n) for n=1..24.

Example

E.g., 21312 (no zero in the string) gives 2+1+3+1+2 = 9 prime factors, namely, 2*2*2*2*2*2*3*3*37.

Mathematica

t={}; Do[If[FreeQ[x=IntegerDigits[n], 0]&&PrimeOmega[n]==Total[x], AppendTo[t, n]], {n, 2, 3220000, 2}]; t (* Jayanta Basu, May 30 2013 *)

Crossrefs

Cf. A050689, A057531, A057532, A070274, A070275, A063737, A067077.

Sequence in context: A045660 A334307 A192213 * A079561 A328326 A131543

Adjacent sequences: A050687 A050688 A050689 * A050691 A050692 A050693

Keyword

nonn,base,nice,hard

Author

Patrick De Geest, Aug 15 1999

Extensions

a(15)-a(20) from Donovan Johnson, May 30 2010

a(21)-a(22) confirmed by Giovanni Resta, Jun 02 2013

a(23)-a(24) from Giovanni Resta, Apr 23 2017

Status

approved