The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A014575 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A014575

Vampire numbers (definition 2): numbers n with an even number of digits which have a factorization n = i*j where i and j have the same number of digits and the multiset of the digits of n coincides with the multiset of the digits of i and j.
(history; published version)

#79 by Michel Marcus at Sun Aug 04 16:39:04 EDT 2024

STATUS

reviewed

approved

#78 by Andrew Howroyd at Sun Aug 04 16:37:27 EDT 2024

STATUS

proposed

reviewed

#77 by Jason Yuen at Sun Aug 04 16:14:58 EDT 2024

STATUS

editing

proposed

#76 by Jason Yuen at Sun Aug 04 16:14:53 EDT 2024

PROG

(PARI) is_A014575(n)={my(v=vecsort(Vecsmall(Str(n)))); #v%2 && return; my( M=10^(#v\2), L=M\10); fordiv(n, d, d<L && next; d<M || return; v==vecsort(Vecsmall(Str(d, n/d))) && return(d)) } \\ Twice as fast. Returns smallest factor (A048933) if vampire number, or false (empty, 0) else. - M. F. Hasler, Mar 11 2021

STATUS

approved

editing

#75 by Sean A. Irvine at Sat Mar 25 16:33:23 EDT 2023

STATUS

proposed

approved

#74 by Ely Golden at Mon Mar 06 09:05:09 EST 2023

STATUS

editing

proposed

#73 by Ely Golden at Mon Mar 06 09:00:17 EST 2023

LINKS

Ely Golden, <a href="/A014575/a014575_5.sagewspy.txt">General Sympy program for generating vampire number sequencesnumbers (definition 2)</a>

Ely Golden, <a href="/A014575/a014575.py.txt">Sympy program for generating vampire numbers (definition 2)</a>

Discussion

Mon Mar 06

09:05

Ely Golden: Updated program to a sympy version, as per the discussion in A020342.

#72 by Ely Golden at Mon Mar 06 09:00:00 EST 2023

LINKS

Ely Golden, <a href="/A014575/a014575.py.txt">Sympy program for generating vampire numbers (definition 2)</a>

STATUS

approved

editing

#71 by N. J. A. Sloane at Sun Apr 04 01:04:12 EDT 2021

STATUS

proposed

approved

#70 by Michel Marcus at Fri Apr 02 02:00:41 EDT 2021

STATUS

editing

proposed