A271225 - OEIS

A271225

a(n) = (A268924(n)^2 + 2)/3^n, n >= 0.

2, 1, 2, 18, 6, 2, 354, 118, 1107, 369, 123, 41, 239803, 495074, 3475362, 1158454, 7887171, 2629057, 56207062, 246253281, 82084427, 5389722857, 25755119139, 8585039713, 53195580742, 193589999521

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OFFSET

0,1

COMMENTS

a(n) is an integer because b(n) = A268924(n) satisfies b(n)^2 + 2 == 0 (mod 3^n), n >= 0.

See A268924 for details, links and references.

LINKS

Table of n, a(n) for n=0..25.

FORMULA

a(n) = (b(n)^2 + 2)/3^n, n >= 0, with b(n) = A268924(n).

EXAMPLE

a(0) = (0^2 + 2)/1 = 2.

a(4) = (22^2 + 2)/3^4 = 6.

PROG

(PARI) b(n) = 3^n - truncate(sqrt(-2+O(3^(n))));

a(n) = (b(n)^2 + 2)/3^n; \\ Michel Marcus, Apr 09 2016

CROSSREFS

Cf. A268924, A271223, A271226 (companion sequence).

Sequence in context: A058260 A202410 A358495 * A349563 A115507 A343259

Adjacent sequences: A271222 A271223 A271224 * A271226 A271227 A271228

KEYWORD

nonn,easy

AUTHOR

Wolfdieter Lang, Apr 05 2016

STATUS

approved