The On-Line Encyclopedia of Integer Sequences (OEIS)

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A301382 revision #11

A301382

a(1) = 1. For n > 1, a(n) is the smallest positive integer x not already in the sequence such that the product of x and its initial digit is minimal and strictly larger than the same product for any previous term.

1, 2, 3, 10, 11, 12, 13, 14, 15, 4, 17, 18, 19, 5, 6, 20, 21, 22, 23, 24, 7, 25, 26, 27, 28, 29, 8, 9, 30, 31, 32, 33, 100, 101, 34, 103, 104, 35, 106, 107, 36, 109, 110, 37, 112, 113, 38, 115, 116, 39, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

We see in the Example section that P is the smallest possible product strictly bigger than the previous one and not leading to a contradiction.

LINKS

Table of n, a(n) for n=1..69.

Jean-Marc Falcoz, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1) * [the first digit of a(1)] = 1 * 1 = P = 1

a(2) * [the first digit of a(2)] = 2 * 2 = P = 4

a(3) * [the first digit of a(3)] = 3 * 3 = P = 9

a(4) * [the first digit of a(4)] = 10 * 1 = P = 10

a(5) * [the first digit of a(5)] = 11 * 1 = P = 11

a(6) * [the first digit of a(6)] = 12 * 1 = P = 12

a(7) * [the first digit of a(7)] = 13 * 1 = P = 13

a(8) * [the first digit of a(8)] = 14 * 1 = P = 14

a(9) * [the first digit of a(9)] = 15 * 1 = P = 15

a(10) * [the first digit of a(10)] = 4 * 4 = P = 16

a(11) * [the first digit of a(11)] = 17 * 1 = P = 17

Etc.

PROG

(PARI) p = vector(136, k, oo); for (n=1, #p, x = n*digits(n)[1]; if (x<=#p, p[x] = min(p[x], n))); for (k=1, #p, if (p[k] != oo, print1 (p[k] ", "))) \\ Rémy Sigrist, Mar 22 2018

CROSSREFS

Sequence in context: A283436 A225558 A362089 * A288657 A055655 A371030

Adjacent sequences: A301379 A301380 A301381 * A301383 A301384 A301385

KEYWORD

nonn,base

AUTHOR

Eric Angelini and Jean-Marc Falcoz, Mar 20 2018

STATUS

editing