A181287 - OEIS

A181287

Numbers of the form i*5^j-1 (i=1..4, j >= 0).

0, 1, 2, 3, 4, 9, 14, 19, 24, 49, 74, 99, 124, 249, 374, 499, 624, 1249, 1874, 2499, 3124, 6249, 9374, 12499, 15624, 31249, 46874, 62499, 78124, 156249, 234374, 312499, 390624, 781249, 1171874, 1562499, 1953124, 3906249, 5859374, 7812499, 9765624, 19531249, 29296874, 39062499, 48828124, 97656249, 146484374, 195312499

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OFFSET

1,3

COMMENTS

Row numbers of Pascal's Triangle where none of the binomial coefficients in that row is divisible by 5. - Thomas M. Green, Apr 02 2013

LINKS

Table of n, a(n) for n=1..48.

Index entries for linear recurrences with constant coefficients, signature (1,0,0,5,-5).

FORMULA

a(n) = a(n-1)+5*a(n-4)-5*a(n-5). G.f.: x^2*(x+1)*(x^2+1) / ((x-1)*(5*x^4-1)). [Colin Barker, Feb 01 2013]

EXAMPLE

For n = 7, a(7) = 14 and the binomial coefficients in the 14th row of Pascal's Triangle are 1 14 91 364 1001 2002 3003 3432 3003 2002 1001 364 91 14 1 and none of the elements in that row is divisible by 5. - Thomas M. Green, Apr 05 2013

CROSSREFS

Smallest number whose base b sum of digits is n: A000225 (b=2), A062318 (b=3), A180516 (b=4), this sequence (b=5), A181288 (b=6), A181303 (b=7), A165804 (b=8), A140576 (b=9), A051885 (b=10). - Jason Kimberley, Nov 02 2011

Sequence in context: A307403 A220952 A188531 * A082981 A217787 A077906

Adjacent sequences: A181284 A181285 A181286 * A181288 A181289 A181290

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Jan 25 2011

STATUS

approved