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 A134808 Cyclops numbers. 42
 0, 101, 102, 103, 104, 105, 106, 107, 108, 109, 201, 202, 203, 204, 205, 206, 207, 208, 209, 301, 302, 303, 304, 305, 306, 307, 308, 309, 401, 402, 403, 404, 405, 406, 407, 408, 409, 501, 502, 503, 504, 505, 506, 507, 508, 509, 601, 602, 603, 604, 605, 606 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers with middle digit 0, that have only one digit 0, and the total number of digits is odd; the digit 0 represents the eye of a cyclops. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 Brady Haran and Simon Pampena, Glitch Primes and Cyclops Numbers, Numberphile video (2015). EXAMPLE 109 is a cyclops number because 109 has only one digit 0 and this 0 is the middle digit. MATHEMATICA cyclopsQ[n_Integer, b_:10] := Module[{digitList = IntegerDigits[n, b], len, pos0s, flag}, len = Length[digitList]; pos0s = Select[Range[len], digitList[[#]] == 0 &]; flag = OddQ[len] && (Length[pos0s] == 1) && (pos0s == {(len + 1)/2}); Return[flag]]; Select[Range[0, 999], cyclopsQ] (* Alonso del Arte, Dec 16 2010 *) Reap[Do[id=IntegerDigits[n]; If[Position[id, 0]=={{(Length[id]+1)/2}}, Sow[n]], {n, 0, 10^3}]][[2, 1]] (* Zak Seidov, Dec 17 2010 *) cycQ[n_]:=Module[{idn=IntegerDigits[n], len=IntegerLength[n]}, OddQ[len] && DigitCount[ n, 10, 0]==1&&idn[[(len+1)/2]]==0]; Join[{0}, Select[Range[ 0, 700], cycQ]] (* Harvey P. Dale, Mar 07 2020 *) PROG (Sage) def is_cyclops(n, base=10): dg = n.digits(base) if n > 0 else [0] return len(dg) % 2 == 1 and dg[len(dg)//2] == 0 and dg.count(0) == 1 is_A134808 = lambda n: is_cyclops(n) # D. S. McNeil, Dec 17 2010 (PARI) a(n, {base=10}) = my (l=0); my (r=n-1); while (r >= (base-1)^(2*l), r -= (base-1)^(2*l); l++); return (base^(l+1) * ( (base^l-1)/(base-1) + if (base>2, fromdigits(digits(r \ ((base-1)^l), (base-1)), base)) ) + ( (base^l-1)/(base-1) + if (base>2, fromdigits(digits(r % ((base-1)^l), (base-1)), base)))) \\ Rémy Sigrist, Apr 29 2017 (Python) from itertools import product def cyclops(upto=float('inf'), upton=float('inf')): # generator yield 0 c, n, half_digits, pow10 = 0, 1, 0, 10 while 100**(half_digits+1) < upto and n < upton: half_digits += 1 pow10 *= 10 for left in product("123456789", repeat=half_digits): left_plus_eye = int("".join(left))*pow10 for right in product("123456789", repeat=half_digits): c, n = left_plus_eye + int("".join(right)), n+1 if c <= upto and n <= upton: yield c print([c for c in cyclops(upto=606)]) print([c for c in cyclops(upton=52)]) # Michael S. Branicky, Jan 05 2021 CROSSREFS Cf. A134809, A138131, A138148, A160717, A182809. Sequence in context: A152054 A296883 A183086 * A274612 A261448 A213312 Adjacent sequences: A134805 A134806 A134807 * A134809 A134810 A134811 KEYWORD base,easy,nonn AUTHOR Omar E. Pol, Nov 21 2007 STATUS approved

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Last modified May 18 15:11 EDT 2024. Contains 372653 sequences. (Running on oeis4.)