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7-smooth numbers (A002473) using digits in descending order. Zero is followed by a 9.
1

%I #19 Sep 19 2024 14:42:08

%S 1,2,3,4,5,6,7,8,9,10,21,32,54,98,210,432

%N 7-smooth numbers (A002473) using digits in descending order. Zero is followed by a 9.

%C No more terms < 10^1000. Probably no more terms. - _David Wasserman_, Feb 10 2005

%e 432 is a member as 432= 2^4*3^3.

%o (PARI) hcn(n) = while (!(n%2), n \=2); while (!(n%3), n \=3); while (!(n%5), n \=5); while (!(n%7), n \=7); n == 1;

%o for (i = 0, 1000, for (j = 1, 9, my(n = sum(k = j - i, j, (k%10)*10^(i - j + k))); if (hcn(n), print1(n, ", ")))); /* _David Wasserman_, Feb 10 2005 */

%Y Intersection of A002473 and A158699.

%Y Cf. A085889.

%K base,nonn

%O 1,2

%A _Amarnath Murthy_ and Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jul 10 2003

%E More terms from _David Wasserman_, Feb 10 2005