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 A294893 Number of divisors d of n such that Stern polynomial B(d,x) is irreducible. 6
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS Number of terms > 1 of A186891 that divide n. LINKS Antti Karttunen, Table of n, a(n) for n = 1..22001 FORMULA a(n) = Sum_{d|n} A283991(d). a(n) + A294894(n) = A000005(n). a(n) = A294891(n) + A283991(n). EXAMPLE For n=25, with divisors [1, 5, 25], both B(5,x) and B(25,x) are irreducible, thus a(25)=2. PROG (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)); CROSSREFS Cf. A186891, A283991, A294891, A294892, A294894. Cf. also A294883. Differs from A001221 for the first time at n=25. Sequence in context: A259936 A050320 A333175 * A336570 A121382 A305150 Adjacent sequences:  A294890 A294891 A294892 * A294894 A294895 A294896 KEYWORD nonn AUTHOR Antti Karttunen, Nov 10 2017 STATUS approved

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Last modified July 31 23:46 EDT 2021. Contains 346377 sequences. (Running on oeis4.)