|
%I #19 Sep 08 2016 03:59:30
%S 2,3,5,7,3,5,7,11,13,17,19,2,3,5,7,11,13,17,19,5,7,11,13,17,19,23,7,
%T 11,13,17,19,23,11,13,17,19,23,7,13,19,3,5,11,17,23,29,7,13,19,31,11,
%U 17,23,29,13,19,31,37,17,23,29,41,19,31,37,43,2,5,11,17,23,29,7,13,19,31,11
%N Primes appearing as the products of digits and positions in A156207(i) in the order of appearance.
%C A156207 read without the 1's and without the composites. - _R. J. Mathar_, Sep 07 2016
%H Robert Israel, <a href="/A156208/b156208.txt">Table of n, a(n) for n = 1..10000</a>
%F Given a number n with digits d1d2d3...dm, a(n) = d1*1+d2*2+d3*3+...+dm*m.
%F If a(n) is prime, list it.
%e For n=19 we have 1*1 + 2*9 = 19 prime and the sequence.
%p f:= proc(n) local L,i,a;
%p L:= convert(n,base,10);
%p a:= add(L[-i]*i,i=1..nops(L));
%p if isprime(a) then a else NULL fi
%p end proc:
%p map(f, [$1..1000]); # _Robert Israel_, Sep 07 2016
%o (PARI) g1(n) = for(j=1,n,if(isprime(g(j)),print1(g(j)",")))
%o g(n) = v=Vec((Str(n)));sum(x=1,length(v),x*eval(v[x]))
%Y Cf. A156207.
%K base,nonn,less
%O 1,1
%A _Cino Hilliard_, Feb 05 2009, Feb 08 2009
%E Definition clarified. - _R. J. Mathar_, Sep 07 2016
|
