A218005 Nonsquare semiprimes p*q (10 excluded) giving record large smallest number p^r * q^s such that each decimal digit appears a prime number of times.

6, 14, 15, 33, 57, 185, 237, 247, 291, 327, 403

Offset: 1

Author

James G. Merickel, Oct 17 2012

Keywords

• nonn
• base
• obsc
• more

Comments

The idea for this sequence derives from A216854 and A217404 through A217433. 10 is excluded as a special case, as it necessitates finding the smaller of powers of 2 and 5 to have no digit other than 0 not appearing a prime number of times (to then be multiplied by the first power of 10 to give prime count for this digit). Even the sparser sets of mere prime powers should have members satisfying the criterion; but the numbers can be quite large, and at time of submission the actual record value for this sequence's a(11) (13*31) is unknown. The record values to that point are: (2^56)*(3^12), (2^36)*(7^15), (3^35)*(5^17), (3^29)*(11^22), (3^24)*(19^22), (5^30)*(37^12), (3^48)*(79^9), (13^40)*(19^4), (3^16)*(97^26), and (3^248)*(109^244).

Crossrefs

Cf. A216854, A217404, A217407, A217410, A217413, A217416, A217419, A217422, A217425, A217428, A217431.