A323639 -id:A323639

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A322571

Positive integers A270710(k) (= (k+1)*(3*k-1)) which have only 1 or 2 different digits in base 10.

+10
2

4, 15, 32, 55, 84, 119, 455, 799, 900, 3332, 3535, 7007, 8855, 244244, 333332, 335335, 400404, 445444, 555559, 666464, 799799, 1999199, 3303300, 33333332, 33353335, 3333333332, 3333533335, 333333333332, 333335333335, 700007077007, 33333333333332, 33333353333335, 3333333333333332, 3333333533333335

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OFFSET

1,1

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..50

FORMULA

a(n) = A270710(A322570(n)).

For k > 0, A002277(2*k) - 1 is a term.

MATHEMATICA

Select[Table[(n+1)(3n-1), {n, 3334*10^4}], Count[DigitCount[#], 0]>7&] (* Harvey P. Dale, Jun 12 2022 *)

PROG

(PARI) for(k=1, 1e8, if(#Set(digits(j=3*k^2+2*k-1))<=2, print1(j", ")))

(Magma) [a:k in [1..10000000]| #Set(Intseq(a)) le 2 where a is (k+1)*(3*k-1)]; // Marius A. Burtea, Aug 29 2019

CROSSREFS

Cf. A002277, A018885 (in case of squares), A213516 (in case of triangular numbers), A270710, A322570, A323639.

KEYWORD

nonn,base

AUTHOR

Seiichi Manyama, Aug 29 2019

STATUS

approved

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