A391117 - OEIS

%I #33 Jan 30 2026 17:39:37

%S 1,49,343,2401,823543,33232930569601,3909821048582988049,

%T 191581231380566414401,909543680129861140820205019889143

%N Powers of 7 that do not contain the digit 7 (in base 10).

%C All terms in A013786 will not be in this sequence.

%C This sequence is probably finite.

%C No further terms 7^k, k <= 5*10^6. - _Sean A. Irvine_, Jan 30 2026

%t Select[7^Range[0, 100000], Not[MemberQ[IntegerDigits[#], 7]]&]

%o (Python)

%o def sequence_terms(count):

%o     terms = []

%o     k = 0

%o     while len(terms) < count:

%o         v = 7 ** k

%o         if '7' not in str(v):

%o             terms.append(v)

%o         k += 1

%o     return terms

%o print(sequence_terms(9))

%Y Intersection of A000420 and A052419.

%Y Cf. A013786.

%Y Cf. A136291 (row 7), A185186.

%K nonn,base

%O 1,2

%A _Amelie King_, Jan 25 2026