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A262007 G.f.: Sum_{n=-oo..+oo} x^n * (1 - x^n)^n / (1 - x)^n. 2
1, 2, 1, 8, 7, 27, 45, 102, 194, 439, 844, 1775, 3608, 7342, 14891, 30283, 61113, 123625, 249355, 502430, 1011305, 2034028, 4086860, 8206874, 16469851, 33035697, 66234208, 132746099, 265961186, 532718115, 1066778721, 2135822309, 4275459594, 8557335615, 17125445126, 34268966022, 68568212859, 137187104632 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Compare to the curious identity: Sum_{n=-oo..+oo} x^n * (1 - x^n)^n = 0.

Compare also to the g.f. of A077229, where A077229(n) equals the number of compositions of n where the largest part is <= the number of parts.

LINKS

Paul D. Hanna, Table of n, a(n) for n = 1..1000

FORMULA

G.f.: Sum_{n=-oo..+oo} (-1)^n * x^(n^2-n) * (1 - x)^n / (1 - x^n)^n.

Limit a(n)^(1/n) = 2.

a(n) ~ 2^(n-1). - Vaclav Kotesovec, Sep 03 2017

EXAMPLE

G.f.: A(x) = x + 2*x^2 + x^3 + 8*x^4 + 7*x^5 + 27*x^6 + 45*x^7 + 102*x^8 + 194*x^9 + 439*x^10 + 844*x^11 + 1775*x^12 +...

such that A(x) = N(x) + P(x) where

N(x) = Sum_{n>=1} (-1)^n * x^(n^2-n) * (1 - x)^n / (1 - x^n)^n

P(x) = Sum_{n>=0} x^n * (1 - x^n)^n / (1 - x)^n.

Explicitly,

N(x) = -1 + x^2 - 2*x^3 + 3*x^4 - 4*x^5 + 4*x^6 - 3*x^7 + 4*x^8 - 10*x^9 + 18*x^10 - 19*x^11 + 9*x^12 + 2*x^13 + x^14 - 22*x^15 + 50*x^16 +...

P(x) = 1 + x + x^2 + 3*x^3 + 5*x^4 + 11*x^5 + 23*x^6 + 48*x^7 + 98*x^8 + 204*x^9 + 421*x^10 + 863*x^11 + 1766*x^12 + 3606*x^13 + 7341*x^14 + 14913*x^15 + 30233*x^16 +...+ A077229(n)*x^n +...

PROG

(PARI) {a(n) = local(A=1);

A = sum(k=-n-1, n+1, x^k * (1-x^k)^k / (1-x +x*O(x^n))^k); polcoeff(A, n)}

for(n=1, 31, print1(a(n), ", "))

(PARI) {a(n) = local(A=1);

A = sum(k=-n-1, n+1, (-1)^k * x^(k^2-k) * (1 - x)^k / (1 - x^k +x*O(x^n))^k); polcoeff(A, n)}

for(n=1, 31, print1(a(n), ", "))

CROSSREFS

Cf. A077229, A260147.

Sequence in context: A105672 A338249 A214271 * A005489 A015152 A021461

Adjacent sequences:  A262004 A262005 A262006 * A262008 A262009 A262010

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Sep 21 2015

STATUS

approved

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Last modified June 17 05:18 EDT 2021. Contains 345080 sequences. (Running on oeis4.)