A061585 a(1) = 1, a(n)= number obtained by replacing each digit of a(n-1) with seven times its value.

1, 7, 49, 2863, 14564221, 72835422814147, 49145621352814145672872849, 286372835421472135145672872835424914564914562863, 1456422149145621352814728491472135728354249145649145621352814286372835422863728354214564221

Offset: 1

Author

Amarnath Murthy, May 13 2001

Keywords

• nonn
• base
• easy

Links

• John Cerkan, Table of n, a(n) for n = 1..12

Crossrefs

Cf. A061581, A061582, A061583, A061584, A061586, A061587.

Programs

Mathematica

NestList[FromDigits[Flatten[IntegerDigits/@(7*IntegerDigits[#])]]&,1,10] (* Harvey P. Dale, Jan 23 2015 *)

PARI

A061585(n=2,a=1,m=7)={while(n--,a=eval(concat(apply(t->Str(t),digits(a)*m))));a} \\ If only the 2nd argument is given, then the operation is applied once to that argument. - M. F. Hasler, Jun 24 2016

Python

def A061585_first(n):
    an = "1"
    a061585 = []
    while n > 1:
        a061585.append(int(an))
        newan = ""
        for i in an:
            newan += str(7*int(i))
        an = newan
        n -= 1
    a061585.append(int(an))
    return a061585 # John Cerkan, May 25 2018

Extensions

More terms from Larry Reeves (larryr(AT)acm.org) and Asher Auel, May 15 2001

Corrected by Harvey P. Dale, Jan 23 2015