A176543 - OEIS

%I #10 Feb 06 2019 01:59:00

%S 7,36,44,63,68,79,128,148,157,192,244,303,323,335,410,421,475,483,535,

%T 606,616,669,776,849,862,868,947,964,986,1039,1046,1256,1264,1403,

%U 1406,1422,1579,1700,1733,1874,1971

%N Numbers k such that semiprime(k)/sum of digits of semiprime(k) is prime.

%F A001358(a(n))/A175013(a(n)) is prime.

%e 7 is a term because 7 (prime) = 21/3 = semiprime(7)/sum of digits of semiprime(7);

%e 36 is a term because 37 (prime) = 111/3 = semiprime(36)/sum of digits of semiprime(36).

%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 2000 do r := A001358(n)/A175013(n) ; if type(r,'integer') then if isprime(r) then printf("%d,",n) ; end if; end if; end do: # _R. J. Mathar_, Apr 26 2010

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

%K nonn,base,less

%O 1,1

%A _Juri-Stepan Gerasimov_, Apr 20 2010

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