A154568 - OEIS

%I #8 Feb 10 2019 11:52:48

%S 8,10,15,18,14,12,6,9,12,15,22,16,10,20,16,10,18,21,8,14,10,20,22,16,

%T 21,26,15,22,16,18,21,26,15,24,18,14,21,15,24,22,30,20,22,15,18,20,27,

%U 26,26,24,27,34,34,21,21,22,25,32,32,28,22,27,27,36,30,25,28,18,20,18,25

%N Composites of the form (sum of digits of k) + (sum of digits of prime(k)).

%e Prime(3) = 5 and 3 + 5 = 8 is composite, so 8 is a term;

%e prime(6) = 13 and 6 + 1 + 3 = 10 is composite, so 10 is a term.

%p A007953 := proc(n) add(d,d=convert(n,base,10)) ; end proc:

%p for n from 1 to 300 do a := A007953(n) +A007953(ithprime(n)) ; if a> 4 and not isprime(a) then printf("%d,",a ) ; end if; end do: # _R. J. Mathar_, May 05 2010

%Y Cf. A000040, A002808.

%K nonn,base

%O 1,1

%A _Juri-Stepan Gerasimov_, Jan 12 2009

%E Corrected (a(36) changed, a(48) inserted etc.) by _R. J. Mathar_, May 05 2010