OFFSET
1,1
COMMENTS
Conjecture: no term is zero.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..10000
FORMULA
a(10*n) = a(n)*10. - Chai Wah Wu, Aug 11 2017
EXAMPLE
a(19) = 133 = 19*7 and 1*3*3 = 1*9.
PROG
(Python)
from functools import reduce
from operator import mul
def A087304(n):
i, p = 2, reduce(mul, (int(d) for d in str(n) if d != '0'))
while (max(str(i)) == '1' and str(i).count('1') == 1) or reduce(mul, (int(d) for d in str(i*n) if d != '0')) != p:
i += 1
return i*n # Chai Wah Wu, Aug 11 2017
(PARI) prd(n) = {my(d = digits(n), p = 1); for (k=1, #d, if (d[k], p *= d[k]); ); p; }
a(n) = {my(k = 2, prdn = prd(n)); while (prd(k*n) != prdn, k++; if (! (k % 10), k++)); k*n; } \\ Michel Marcus, Aug 12 2017
CROSSREFS
KEYWORD
AUTHOR
Amarnath Murthy, Sep 01 2003
EXTENSIONS
More terms from David Wasserman, Apr 19 2005
STATUS
approved