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A083951 Least increasing integer coefficients such that A(x)^(1/3) has only integer coefficients. 1
1, 3, 6, 7, 9, 12, 13, 15, 18, 21, 24, 27, 28, 30, 33, 34, 36, 39, 41, 42, 45, 47, 48, 51, 52, 54, 57, 60, 63, 66, 69, 72, 75, 77, 78, 81, 83, 84, 87, 88, 90, 93, 94, 96, 99, 100, 102, 105, 108, 111, 114, 116, 117, 120, 121, 123, 126, 127, 129, 132, 133, 135, 138, 139 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

a(k) == 1 (mod 3) at k=0,3,6,12,15,24,39,42,45,54,57,60,63,66,... a(k) == 2 (mod 3) at k=18,21,33,36,51,...

LINKS

Robert G. Wilson v, Table of n, a(n) for n = 0..5000.

MATHEMATICA

a[0] = 1; a[n_] := a[n] = Block[{k = a[n - 1] + 1, s = Sum[ a[i]*x^i, {i, 0, n - 1}]}, While[ IntegerQ[ Last[ CoefficientList[ Series[(s + k*x^n)^(1/3), {x, 0, n}], x]]] != True, k++ ]; k]; Array[ a, 70] (* Robert G. Wilson v, Sep 19 2008 *)

CROSSREFS

Cf. A083349, A083953.

Sequence in context: A082847 A047242 A190335 * A284879 A208327 A131392

Adjacent sequences:  A083948 A083949 A083950 * A083952 A083953 A083954

KEYWORD

nonn

AUTHOR

Paul D. Hanna, May 09 2003

EXTENSIONS

Three non-ascending values in the range 77 to 84 replaced with those from the b-file. - R. J. Mathar, Jan 14 2009

STATUS

approved

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Last modified May 22 14:32 EDT 2019. Contains 323480 sequences. (Running on oeis4.)