[go: up one dir, main page]

login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A046075
Nontrivial undulants; base 10 numbers >100 which are of the form aba, abab, ababa, ..., where a != b.
11
101, 121, 131, 141, 151, 161, 171, 181, 191, 202, 212, 232, 242, 252, 262, 272, 282, 292, 303, 313, 323, 343, 353, 363, 373, 383, 393, 404, 414, 424, 434, 454, 464, 474, 484, 494, 505, 515, 525, 535, 545, 565, 575, 585, 595, 606, 616, 626, 636, 646, 656
OFFSET
1,1
REFERENCES
C. A. Pickover, ``The Undulation of the Monks.'' Ch. 20 in Keys to Infinity. New York: W.H.Freeman, pp. 159-161 1995.
C. A. Pickover, "Wonders of Numbers", Oxford New York 2001, Chapter 52, pp. 123-124, 316-317.
LINKS
C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review
Eric Weisstein's World of Mathematics, Undulating Number
PROG
(Haskell)
import Data.Set (fromList, deleteFindMin, insert)
a046075 n = a046075_list !! (n-1)
a046075_list = f $ fromList
[100 * a + 10 * b + a | a <- [1..9], b <- [0..9], b /= a]
where f s = m : f (insert (10 * m + div (mod m 100) 10) s')
where (m, s') = deleteFindMin s
-- Reinhard Zumkeller, Apr 29 2015, May 01 2012
CROSSREFS
Cf. A252664.
Sequence in context: A084430 A182693 A328996 * A088882 A261453 A135602
KEYWORD
nonn,base
STATUS
approved