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A048937 Numbers n with an even number of digits, n = d_1 d_2 ... d_n, such that there are exactly three ways to partition the digits into two groups of size n/2, say f_1 ... f_{n/2} and g_1 ... g_{n/2}, such that n = f_1 ... f_{n/2} * g_1 ... g_{n/2}. 2

%I #16 Feb 15 2015 00:51:52

%S 13078260,107650322640,113024597400,119634515208,134549287600,

%T 135173486250,138130447950,146083269717,150967233648,216315684000,

%U 221089445500,315987404670,463997983680,472812953760,10174695862032,10178463985200,10185571893960,10476754939728,10624657891320

%N Numbers n with an even number of digits, n = d_1 d_2 ... d_n, such that there are exactly three ways to partition the digits into two groups of size n/2, say f_1 ... f_{n/2} and g_1 ... g_{n/2}, such that n = f_1 ... f_{n/2} * g_1 ... g_{n/2}.

%C f_{n/2} and g_{n/2} may not both be zero.

%C Vampire numbers (definition 2) having exactly three distinct pairs of fangs.

%D C. A. Pickover, "Vampire Numbers." Ch. 30 in Keys to Infinity. New York: Wiley, pp. 227-231, 1995.

%H Walter Schneider, <a href="http://web.archive.org/web/2004/www.wschnei.de/digit-related-numbers/vampire.html">Vampire numbers</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/VampireNumber.html">Vampire Number.</a>

%e 13078260 = 1620*8073 = 1863*7020 = 2070*6318; 107650322640 = 153204*702660 = 140532*766020 = 200760*536214.

%Y Cf. A014575, A048933, ..., A048939.

%K nonn,base

%O 1,1

%A _Eric W. Weisstein_

%E More terms found by Walter Schneider, Feb 11 2002 and communicated by _Hans Havermann_, Oct 10 2002

%E More terms from _Jens Kruse Andersen_, Dec 01 2002

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Last modified April 25 05:18 EDT 2024. Contains 371964 sequences. (Running on oeis4.)