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

Author

Patrick De Geest, Aug 15 1999

Keywords

• nonn
• base
• nice
• hard

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

Examples

			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.
		

Crossrefs

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

Programs

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 *)

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