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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
13078260, 107650322640, 113024597400, 119634515208, 134549287600, 135173486250, 138130447950, 146083269717, 150967233648, 216315684000, 221089445500, 315987404670, 463997983680, 472812953760, 10174695862032, 10178463985200, 10185571893960, 10476754939728, 10624657891320 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
f_{n/2} and g_{n/2} may not both be zero.
Vampire numbers (definition 2) having exactly three distinct pairs of fangs.
REFERENCES
C. A. Pickover, "Vampire Numbers." Ch. 30 in Keys to Infinity. New York: Wiley, pp. 227-231, 1995.
LINKS
Walter Schneider, Vampire numbers
Eric Weisstein's World of Mathematics, Vampire Number.
EXAMPLE
13078260 = 1620*8073 = 1863*7020 = 2070*6318; 107650322640 = 153204*702660 = 140532*766020 = 200760*536214.
CROSSREFS
Cf. A014575, A048933, ..., A048939.
Sequence in context: A237034 A210182 A210412 * A257269 A283274 A343083
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
More terms found by Walter Schneider, Feb 11 2002 and communicated by Hans Havermann, Oct 10 2002
More terms from Jens Kruse Andersen, Dec 01 2002
STATUS
approved

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Last modified December 10 04:38 EST 2023. Contains 367699 sequences. (Running on oeis4.)