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 A257210 Numbers n such that the decimal expansions of both n and n^2 have 1 as smallest digit and 7 as largest digit. 16
 271, 371, 1171, 1474, 1475, 1776, 2171, 2271, 2671, 2715, 2761, 3671, 3711, 4174, 4761, 4771, 6761, 7165, 7174, 7261, 7331, 11275, 11474, 11475, 11711, 11715, 11716, 11724, 11725, 11731, 12376, 12715, 12734, 12756, 12776, 13171, 13174, 13275, 13276, 14674 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS There are 2 3-digit terms, 19 4-digit terms, 122 5-digit terms, 646 6-digit terms, 3147 7-digit terms, 13300 8-digit terms, 54689 9-digit terms, and 216858 10-digit terms. - Charles R Greathouse IV, Apr 20 2015 LINKS Felix Fröhlich, Table of n, a(n) for n = 1..10000 MATHEMATICA fQ[n_] := Block[{d = DigitCount@ n}, Plus @@ Take[d, {8, 10}] == 0 && d[[1]] > 0 && d[[7]] > 0]; Select[Range@ 15000, fQ@ # && fQ[#^2] &] (* Michael De Vlieger, Apr 20 2015 *) PROG (PARI) is(n) = vecmin(digits(n))==1 && vecmin(digits(n^2))==1 && vecmax(digits(n))==7 && vecmax(digits(n^2))==7 (PARI) has(n)=my(d=Set(digits(n))); #d && d[1]==1 && d[#d]==7 is(n)=has(n) && has(n^2) for(d=3, 7, for(i=6, 7^d-1, v=digits(i, 7); if(#v<=d, v=concat(vector(d-#v), v)); if(vecmax(v)==6 && vecmin(v)==0 && has((n=fromdigits(apply(k->k+1, v)))^2), print1(n", ")))) \\ Charles R Greathouse IV, Apr 20 2015 CROSSREFS Cf. A256630, A256631, A256633, A256634, A256708, A256709, A256889, A257197, A257211. Sequence in context: A086003 A174402 A048295 * A020363 A051965 A142762 Adjacent sequences:  A257207 A257208 A257209 * A257211 A257212 A257213 KEYWORD nonn,base AUTHOR Felix Fröhlich, Apr 18 2015 STATUS approved

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Last modified June 21 03:09 EDT 2021. Contains 345351 sequences. (Running on oeis4.)