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

1,1

Comments

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

Links

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

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.

Example

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

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

Prog

(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]))

Crossrefs

Cf. A156207.

Sequence in context: A143950 A108534 A039706 * A239695 A073034 A239037

Adjacent sequences: A156205 A156206 A156207 * A156209 A156210 A156211

Keyword

base,nonn,less

Author

Cino Hilliard, Feb 05 2009, Feb 08 2009

Extensions

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

Status

approved