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A265408 Prime factorization representation of Spironacci polynomials: a(0) = 1, a(1) = 2, and for n > 1, a(n) = A003961(a(n-1)) * a(A265409(n)). 5
1, 2, 3, 5, 7, 11, 13, 17, 38, 138, 870, 9765, 213675, 4309305, 201226025, 9679967297, 810726926009, 40855897091009, 4259653632223561, 380804291082185737, 44319264099050115071, 4644246052673250585913 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The polynomials encoded by these numbers could also be called "Fernandez spiral polynomials" after Neil Fernandez who discovered sequence A078510 which is obtained when they are evaluated at X=1.

The polynomial recurrence uses the same composition rules as the Fibonacci polynomials (A206296), but with the neighborhood rules of A078510, where the other polynomial is taken from the nearest inner neighbor (A265409) when the polynomials are arranged as a spiral into a square grid. See A265409 for the illustration.

LINKS

Table of n, a(n) for n=0..21.

FORMULA

a(0) = 1, a(1) = 2, and for n >= 2, a(n) = A003961(a(n-1)) * a(A265409(n)).

Other identities. For all n >= 0:

A078510(n) = A001222(a(n)). [When each polynomial is evaluated at x=1.]

A265407(n) = A248663(a(n)). [at x=2 over the field GF(2).]

EXAMPLE

n    a(n)   prime factorization    Spironacci polynomial

------------------------------------------------------------

0       1   (empty)                S_0(x) = 0

1       2   p_1                    S_1(x) = 1

2       3   p_2                    S_2(x) = x

3       5   p_3                    S_3(x) = x^2

4       7   p_4                    S_4(x) = x^3

5      11   p_5                    S_5(x) = x^4

6      13   p_6                    S_6(x) = x^5

7      17   p_7                    S_7(x) = x^6

8      38   p_8 * p_1              S_8(x) = x^7 + 1

9     138   p_9 * p_2 * p_1        S_9(x) = x^8 + x + 1

PROG

(Scheme, with memoization-macro definec)

(definec (A265408 n) (cond ((<= n 1) (+ 1 n)) (else (* (A003961 (A265408 (- n 1))) (A265408 (A265409 n))))))

CROSSREFS

Cf. A003961, A265407, A265409.

Cf. also A078510, A206296 and A265752, A265753.

Sequence in context: A016114 A263499 A258706 * A053434 A241716 A061166

Adjacent sequences:  A265405 A265406 A265407 * A265409 A265410 A265411

KEYWORD

nonn

AUTHOR

Antti Karttunen, Dec 13 2015

STATUS

approved

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Last modified June 18 14:52 EDT 2019. Contains 324213 sequences. (Running on oeis4.)