A176544 - OEIS

%I #15 Aug 10 2023 11:06:07

%S 7,37,19,67,19,19,37,37,73,37,73,337,367,163,73,109,127,73,109,163,

%T 127,181,163,433,181,163,199,181,271,163,199,199,271,271,397,307,307,

%U 487,379,541,433,577,397,271,631,433,379,487,919,1459,541,937,811,631,991

%N Primes of the form semiprime(k)/sum of digits of semiprime(k).

%H Harvey P. Dale, <a href="/A176544/b176544.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = p = A001358(n)/A175013(n).

%F a(n) = A001358(A176543(n))/A175013(A176543(n)). - _R. J. Mathar_, Apr 26 2010

%e 7 is a term because 7 = 21/(2+1);

%e 37 is a term because 37 = 111/(1+1+1).

%p A175013 := proc(n) A007953(A001358(n)) ; end proc: A007953 := proc(n) add(d,d=convert(n,base,10)) ; end proc: for n from 1 to 4000 do r := A001358(n)/A175013(n) ; if type(r,'integer') then if isprime(r) then printf("%d,",r) ; end if; end if; end do: # _R. J. Mathar_, Apr 26 2010

%t Select[#/Total[IntegerDigits[#]]&/@Select[Range[30000],PrimeOmega[#]==2&],PrimeQ] (* _Harvey P. Dale_, Aug 10 2023 *)

%Y Cf. A001358 (semiprimes), A007953 (sum of digits), A175013, A176543.

%K nonn,base

%O 1,1

%A _Juri-Stepan Gerasimov_, Apr 20 2010

%E More terms from _R. J. Mathar_, Apr 26 2010