A117718 - OEIS

A117718

Number of heptagonal numbers with n digits.

3, 4, 14, 43, 137, 432, 1368, 4324, 13676, 43245, 136755, 432455, 1367545, 4324555, 13675445, 43245553, 136754447, 432455532, 1367544468, 4324555320, 13675444680, 43245553203, 136754446797, 432455532033, 1367544467967

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OFFSET

0,1

LINKS

Table of n, a(n) for n=0..24.

EXAMPLE

a(4)=43 because there are 43 heptagonal numbers with 4 digits.

MAPLE

Digits := 20: A117718 := proc(n) if n = 1 then 3; else ceil(3/10*(1+sqrt(1+40*10^n/9))-1) - ceil(3/10*(1+sqrt(40*10^(n-1)/9))) +1 ; fi ; end: seq(A117718(n), n=1..30) ; # R. J. Mathar, Jan 22 2008

CROSSREFS

Cf. A000566.

Sequence in context: A057433 A006074 A081714 * A268700 A349001 A176857

Adjacent sequences: A117715 A117716 A117717 * A117719 A117720 A117721

KEYWORD

base,nonn

AUTHOR

Luc Stevens (lms022(AT)yahoo.com), Apr 13 2006

EXTENSIONS

More terms from R. J. Mathar, Jan 22 2008

STATUS

approved