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
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
KEYWORD
nonn,base
AUTHOR
Eric Angelini and Jean-Marc Falcoz, Mar 20 2018
STATUS
approved