A156208 Primes appearing as the products of digits and positions in A156207(i) in the order of appearance.

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, 11, 13, 17, 19, 23, 11, 13, 17, 19, 23, 7, 13, 19, 3, 5, 11, 17, 23, 29, 7, 13, 19, 31, 11, 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

Offset: 1

Author

Cino Hilliard, Feb 05 2009, Feb 08 2009

Keywords

• base
• nonn
• less

Comments

A156207 read without the 1's and without the composites. - R. J. Mathar, Sep 07 2016

Examples

			For n=19 we have 1*1 + 2*9 = 19 prime and the sequence.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A156207.

Programs

Maple

f:= proc(n) local L,i,a;
  L:= convert(n,base,10);
  a:= add(L[-i]*i,i=1..nops(L));
  if isprime(a) then a else NULL fi
end proc:
map(f, [$1..1000]); # Robert Israel, Sep 07 2016

PARI

g1(n) = for(j=1,n,if(isprime(g(j)),print1(g(j)",")))
g(n) = v=Vec((Str(n)));sum(x=1,length(v),x*eval(v[x]))

Formula

Given a number n with digits d1d2d3...dm, a(n) = d1*1+d2*2+d3*3+...+dm*m.

If a(n) is prime, list it.

Extensions

Definition clarified. - R. J. Mathar, Sep 07 2016