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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 Table of n, a(n) for n=1..19. 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 Adjacent sequences: A048934 A048935 A048936 * A048938 A048939 A048940 KEYWORD nonn,base AUTHOR Eric W. Weisstein 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.)