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A280641 Numbers k such that k^3 has an odd number of digits and the middle digit is 1. 3
1, 6, 8, 23, 44, 45, 102, 106, 110, 114, 117, 121, 137, 148, 152, 153, 162, 168, 176, 185, 189, 194, 206, 210, 478, 488, 512, 533, 553, 560, 574, 580, 626, 639, 655, 662, 669, 671, 676, 682, 683, 684, 685, 693, 704, 710, 730, 731, 737, 742, 758, 761, 767, 771 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The sequence of cubes starts: 1, 216, 512, 12167, 85184, 91125, 1061208, 1191016, ...

LINKS

Lars Blomberg, Table of n, a(n) for n = 1..10000

Jeremy Gardiner, Middle digit in cube numbers, Seqfan Mailing list, Dec 12 2016.

EXAMPLE

1^3 = (1), 114^3 = 148(1)544, 560^3 = 1756(1)6000

MATHEMATICA

a[n_]:=Part[IntegerDigits[n], (Length[IntegerDigits[n]] + 1)/2];

Select[Range[0, 771], OddQ[Length[IntegerDigits[#^3]]] && a[#^3]==1 &] (* Indranil Ghosh, Mar 06 2017 *)

PROG

(PARI)

isok(k) = my(d=digits(k^3)); (#d%2 == 1) && (d[#d\2 +1] == 1);

for(k=0, 771, if(isok(k)==1, print1(k, ", "))); \\ Indranil Ghosh, Mar 06 2017

(Python)

i=0

j=1

while i<=771:

    n=str(i**3)

    l=len(n)

    if l%2 and n[(l-1)//2]=="1":

        print(str(i), end=', ')

        j+=1

    i+=1 # Indranil Ghosh, Mar 06 2017

CROSSREFS

Cf. A280640, A280642-A280649, A181354.

See A279420-A279429 for a k^2 version.

See A279430-A279431 for a k^2 version in base 2.

Sequence in context: A276226 A034761 A085796 * A005887 A119875 A053189

Adjacent sequences:  A280638 A280639 A280640 * A280642 A280643 A280644

KEYWORD

nonn,base,easy

AUTHOR

Lars Blomberg, Jan 07 2017

STATUS

approved

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Last modified May 16 08:07 EDT 2021. Contains 343940 sequences. (Running on oeis4.)