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A343536 Positive numbers k such that the decimal expansion of k^2 appears in the concatenation of the first k positive integers. 1
1, 428, 573, 725, 727, 738, 846, 7810, 8093, 28023, 36354, 36365, 36464, 63636, 254544, 277851, 297422, 326734, 673267, 673368, 2889810, 4545454, 4545465, 5454547, 5454646, 24275425, 29411775, 47058823, 52941178, 94117748, 146407310, 263157795, 267735365, 285714186 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A030467 is a subsequence. - Chai Wah Wu, Jun 07 2021

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..116

EXAMPLE

428^2 = 183184, which appears in the concatenation of the first 428 positive integers at 183,184, i.e., (183184), so 428 is a term.

725^2 = 525625, which appears in the concatenation of the first 725 positive integers at 255,256,257, i.e., 25(525625)7, so 725 is a term.

MATHEMATICA

Select[Range@1000, StringContainsQ[""<>ToString/@Range@#, ToString[#^2]]&] (* Giorgos Kalogeropoulos, Apr 24 2021 *)

PROG

(Java)

public class Oeis2 {

    public static void main(String[] args) {

        StringBuilder str = new StringBuilder();

        long n = 1;

        while (true) {

            str.append(n);

            if (str.indexOf(String.valueOf(n * n)) >= 0) {

                System.out.print(n + ", ");

            }

            n++;

        }

    }

}

(PARI) f(n) = my(s=""); for(k=1, n, s=Str(s, k)); s; \\ from A007908

isok(k) = #strsplit(f(k), Str(k^2)) > 1; \\ Michel Marcus, May 02 2021

(Python)

A343536_list, k, s = [], 1, '1'

while k < 10**6:

    if str(k**2) in s:

        A343536_list.append(k)

    k += 1

    s += str(k) # Chai Wah Wu, Jun 06 2021

CROSSREFS

Cf. A007908, A030467, A259379.

Sequence in context: A235217 A236383 A224668 * A030467 A253505 A173798

Adjacent sequences:  A343533 A343534 A343535 * A343537 A343538 A343539

KEYWORD

nonn,base

AUTHOR

John R Phelan, Apr 18 2021

EXTENSIONS

More terms from Jinyuan Wang, Apr 30 2021

STATUS

approved

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Last modified September 23 20:42 EDT 2021. Contains 347617 sequences. (Running on oeis4.)