A048544 Smallest oblong (promic) number containing exactly n 7's.

72, 11772, 771762, 757770, 77677782, 779777700, 7077772770, 778777127772, 7777770777090, 57777777767730, 7777577077877756, 177677777977777980, 17673737777477771772, 677777977779775677756, 1789771777777771777710, 7747977777770507777772, 298777877777767737777770

Offset

1,1

Links

Table of n, a(n) for n=1..17.

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

Crossrefs

Cf. A048543, A002378.

Cf. A048530, A048532, A048534, A048536, A048538, A048540, A048542, A048546, A048548.

Sequence in context: A271192 A271193 A289369 * A295599 A270254 A273629

Adjacent sequences: A048541 A048542 A048543 * A048545 A048546 A048547

Keyword

nonn,base

Author

Patrick De Geest, May 15 1999

Extensions

a(13)-a(17) from Giovanni Resta, Oct 09 2019

Status

approved