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A294893
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Number of divisors d of n such that Stern polynomial B(d,x) is irreducible.
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6
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0, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 2, 1, 2, 2, 2, 1, 2, 1, 3, 1, 1, 2, 2, 2, 2, 1, 2, 2, 2, 1, 3, 1, 2, 2, 2, 1, 2, 1, 3, 2, 2, 1, 2, 3, 2, 2, 2, 1, 3, 1, 2, 2, 1, 3, 3, 1, 2, 2, 3, 1, 2, 1, 2, 3, 2, 3, 3, 1, 2, 1, 2, 1, 3, 2, 2, 2, 2, 1, 3, 3, 2, 2, 2, 3, 2, 1, 2, 2, 3, 1, 3, 1, 2, 3
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OFFSET
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1,6
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COMMENTS
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Number of terms > 1 of A186891 that divide n.
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LINKS
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Antti Karttunen, Table of n, a(n) for n = 1..22001
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FORMULA
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a(n) = Sum_{d|n} A283991(d).
a(n) + A294894(n) = A000005(n).
a(n) = A294891(n) + A283991(n).
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EXAMPLE
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For n=25, with divisors [1, 5, 25], both B(5,x) and B(25,x) are irreducible, thus a(25)=2.
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PROG
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(PARI)
ps(n) = if(n<2, n, if(n%2, ps(n\2)+ps(n\2+1), 'x*ps(n\2)));
A283991(n) = polisirreducible(ps(n));
A294893(n) = sumdiv(n, d, A283991(d));
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CROSSREFS
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Cf. A186891, A283991, A294891, A294892, A294894.
Cf. also A294883.
Differs from A001221 for the first time at n=25.
Sequence in context: A354870 A050320 A333175 * A336570 A121382 A305150
Adjacent sequences: A294890 A294891 A294892 * A294894 A294895 A294896
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KEYWORD
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nonn
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AUTHOR
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Antti Karttunen, Nov 10 2017
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STATUS
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approved
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