A285829 - OEIS

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A285829

Numbers n such that, for any i and j with i >= j >= 0, ds^i(n) divides ds^j(n) (where ds^k denotes the k-th iteration of the digital sum).

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42, 45, 48, 50, 54, 60, 63, 70, 72, 80, 81, 84, 90, 100, 102, 108, 110, 111, 112, 114, 117, 120, 126, 132, 133, 135, 140, 144, 150, 152, 153, 156, 162, 171, 180, 190, 192, 198, 200, 201, 204, 207, 210, 216, 220, 222, 224, 225, 228, 230, 234, 240, 243, 252, 261, 264, 270, 280, 288, 300, 306, 312

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OFFSET

1,2

COMMENTS

All terms are Niven numbers (A005349).

All terms belongs to A234474; the first difference occurs at index 81: a(81) = 312 whereas A234474(81) = 308.

All powers of 10 belong to the sequence, hence the sequence is infinite.

LINKS

Rémy Sigrist, Table of n, a(n) for n = 1..10000

EXAMPLE

The digital sum of 312 is 6, and it divides 312; the digital sum of 6 is 6; hence 312 appears in the sequence.

The digital sum of 308 is 11, which divides 308; however the digital sum of 11 is 2, which does not divide 11; hence 308 is not in the sequence.

PROG

(PARI) is(n) = my (d=sumdigits(n)); if (n==d, return (1)); if (n%d, return (0)); return (is(d))

CROSSREFS

Cf. A005349, A234474.

Sequence in context: A007603 A005349 A234474 * A225780 A225782 A235507

Adjacent sequences: A285826 A285827 A285828 * A285830 A285831 A285832

KEYWORD

nonn,base

AUTHOR

Rémy Sigrist, Apr 27 2017

STATUS

approved