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A156208
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Primes appearing as the products of digits and positions in A156207(i) in the order of appearance.
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1
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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
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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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.
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EXAMPLE
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For n=19 we have 1*1 + 2*9 = 19 prime and the sequence.
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MAPLE
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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:
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PROG
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(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]))
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CROSSREFS
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KEYWORD
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base,nonn,less
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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