A257486 Numbers n such that the decimal expansions of both n and n^2 have 3 as smallest digit and 7 as largest digit.

6734, 67434, 577734, 667334, 745356, 6674334, 6734744, 6756734, 7373376, 7453574, 7466434, 7533576, 66673334, 67345644, 67656734, 74547734, 74656376, 75733576, 666743334, 667335356, 746556344, 5775434474, 6666733334, 6666733576, 6676476434, 7447533576

Offset

1,1

Links

Chai Wah Wu, Table of n, a(n) for n = 1..1000 (n = 71..178 from Giovanni Resta)

Mathematica

fQ[n_] := Block[{d = DigitCount@ n}, Plus @@ Join[Take[d, {1, 2}], Take[d, {8, 10}]] == 0 && d[[3]] > 0 && d[[7]] > 0]; Select[Range@ 1000000, fQ@# && fQ[#^2] &] (* Michael De Vlieger, Apr 27 2015 *)

Prog

(PARI) is(n) = vecmin(digits(n))==3 && vecmin(digits(n^2))==3 && vecmax(digits(n))==7 && vecmax(digits(n^2))==7
(Python)
from itertools import product, repeat
A257486_list = []
for l in range(12):
....for a in product('34567', repeat = l):
........for b in ('4', '5', '6'):
............s = ''.join(a)+b
............if '3' in s and '7' in s:
................n = int(s)
................if {'3', '7'} <= set(str(n**2)) <= {'3', '4', '5', '6', '7'}:
....................A257486_list.append(n) # Chai Wah Wu, May 02 2015

Crossrefs

Cf. A137121, A256630, A256631, A256633, A256634, A256708, A256709, A256889, A257197, A257210, A257211, A256601, A257310, A249915, A257123, A257368, A257485.

Sequence in context: A064160 A249463 A031642 * A345591 A345849 A253230

Adjacent sequences: A257483 A257484 A257485 * A257487 A257488 A257489

Keyword

nonn,base

Author

Felix Fröhlich, Apr 26 2015

Extensions

a(22)-a(26) from Hiroaki Yamanouchi, May 03 2015 (using Chai Wah Wu's b-file)

Status

approved