login
A048544
Smallest oblong (promic) number containing exactly n 7's.
11
72, 11772, 771762, 757770, 77677782, 779777700, 7077772770, 778777127772, 7777770777090, 57777777767730, 7777577077877756, 177677777977777980, 17673737777477771772, 677777977779775677756, 1789771777777771777710, 7747977777770507777772, 298777877777767737777770
OFFSET
1,1
LINKS
Eric Weisstein's World of Mathematics, Pronic Number
MATHEMATICA
With[{pn=2*Accumulate[Range[430000000]]}, Table[Select[pn, DigitCount[#, 10, 7] == n&, 1], {n, 12}]]//Flatten (* Harvey P. Dale, Aug 14 2017 *)
PROG
(Python)
def A048544(n):
k, m = 1, 2
while True:
if str(m).count('7') == n:
return m
k += 1
m += 2*k # Chai Wah Wu, Mar 23 2018
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, May 15 1999
EXTENSIONS
a(13)-a(17) from Giovanni Resta, Oct 09 2019
STATUS
approved