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A156208 Primes appearing as the products of digits and positions in A156207(i) in the order of appearance. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
A156207 read without the 1's and without the composites. - R. J. Mathar, Sep 07 2016
LINKS
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
KEYWORD
base,nonn,less
AUTHOR
Cino Hilliard, Feb 05 2009, Feb 08 2009
EXTENSIONS
Definition clarified. - R. J. Mathar, Sep 07 2016
STATUS
approved

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Last modified March 28 12:59 EDT 2024. Contains 371254 sequences. (Running on oeis4.)