A257310 - OEIS

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A257310

Numbers n such that the decimal expansions of both n and n^2 have 2 as smallest digit and 5 as largest digit.

235, 2335, 23335, 233335, 2333335, 2354235, 23333335, 233333335, 2333333335, 2333524235, 23333333335, 23333524235, 233333333335, 2333333333335, 23333333333335, 233333333333335, 2333333333333335, 23333333333333335, 233333333333333335, 2333333333333333335

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OFFSET

1,1

COMMENTS

Conjecture: a(n) = A137066(n+2) for all n, i.e., this is A137066 without the initial two terms.

(10^(k+1)-1)/3 - 10^k + 2 are terms for k > 1. Conjecture: except for 2354235, 2333524235, and 23333524235, all terms are of this form. - Chai Wah Wu, Sep 10 2017

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..40 (n = 1..31 from Hiroaki Yamanouchi)

MATHEMATICA

fQ[n_] := Block[{d = DigitCount@ n}, Plus @@ Prepend[Take[d, {6, 10}], First@ d] == 0 && d[[2]] > 0 && d[[5]] > 0]; Select[Range@ 1000000, fQ@ # && fQ[#^2] &] (* Michael De Vlieger, Apr 20 2015 *)

PROG

(PARI) is(n) = vecmin(digits(n))==2 && vecmin(digits(n^2))==2 && vecmax(digits(n))==5 && vecmax(digits(n^2))==5

CROSSREFS

Cf. A137066, A256630, A256631, A256633, A256634, A256708, A256709, A256889, A257197, A257210, A257211.

Sequence in context: A068663 A129857 A146092 * A268890 A254676 A146126

Adjacent sequences: A257307 A257308 A257309 * A257311 A257312 A257313

KEYWORD

nonn,base

AUTHOR

Felix Fröhlich, Apr 20 2015

EXTENSIONS

a(11)-a(20) from Hiroaki Yamanouchi, May 04 2015

STATUS

approved