A308961 Numbers k not divisible by 10 such that k^2 and 2*k are in A046030.

2, 7, 97, 997, 9997, 20247, 99997, 999997, 9999997, 99999997, 999999997, 2224745247, 9999999997, 99999999997, 999999999997, 9999999999997, 99999999999997, 999999999999997, 9999999999999997, 99999999999999997

Offset

1,1

Comments

10^j - 3 are terms. Most of the terms so far are of the form 10^j - 3. Are there other terms not of this form besides 2, 20247, and 2224745247?

If k is a term, then primes of the form k*10^j + 1 for j >= A055642(2*k) are in A308917 and primes of the form 10^j + k for j >= A055642(k^2) are in A308917.

Links

Table of n, a(n) for n=1..20.

Crossrefs

Cf. A046030, A055642, A308917.

Sequence in context: A076740 A112290 A072059 * A240696 A102344 A087589

Adjacent sequences: A308958 A308959 A308960 * A308962 A308963 A308964

Keyword

nonn,base

Author

Chai Wah Wu, Jul 04 2019

Extensions

Edited by Max Alekseyev, Jul 13 2019

Status

approved