A322571 Positive integers A270710(k) (= (k+1)*(3*k-1)) which have only 1 or 2 different digits in base 10.

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

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.

Sequence in context: A336607 A321490 A270710 * A110341 A317614 A331761

Adjacent sequences: A322568 A322569 A322570 * A322572 A322573 A322574

Keyword

nonn,base

Author

Seiichi Manyama, Aug 29 2019

Status

approved