A174924 Semiprimes sp(k) = q * r such that sum of digits of sp(k) equals sum of digits of the semiprime index k.

14, 15, 55, 121, 122, 123, 214, 215, 265, 287, 407, 481, 482, 535, 667, 813, 851, 901, 951, 1119, 1149, 1174, 1537, 1538, 1639, 1681, 1961, 2059, 2117, 2165, 2209, 2245, 2246, 2386, 2419, 2458, 2501, 2513, 2537, 2603, 2629, 2641, 2642, 2643, 2807, 2845

Offset: 1

Author

Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Apr 02 2010

Keywords

• base
• nonn
• less

Comments

Numbers of the form q * r where q and r are primes, not necessarily distinct.

These numbers are also called semiprimes or 2-almost primes.

For primes with such a property see A033548

Examples

			sp(5) = 14 = 2 * 7 is the 5th semiprime, sum of digits sod(14) = 1+4 = 5, 1st term
sp(6) = 15 = 3 * 5 is the 6th semiprime, sum of digits sod(15) = 1+5 = 6. 2nd term
sp(40) = 121 = 11^2 is the 40th semiprime, sum of digits sod(121) = 1+2+1 = 4, 4th term
Additionally for the prime based (q=r=11) square 121: sod(q) + sod(r) = 2 * sod(11) = 4
The first 110 such semiprimes:
14, 15, 55, 121, 122, 123, 214, 215, 265, 287, 407, 481, 482, 535, 667, 813, 851, 901, 951, 1119,
1149, 1174, 1537, 1538, 1639, 1681, 1961, 2059, 2117, 2165, 2209, 2245, 2246, 2386, 2419,
2458, 2501, 2513, 2537, 2603, 2629, 2641, 2642, 2643, 2807, 2845, 2846, 2858, 2859, 2921,
3158, 3205, 3218, 3427, 3439, 4322, 4333, 4367, 4661, 4713, 4714, 4735, 4811, 5221, 5317,
5318, 5615, 5707, 5753, 6009, 6022, 6023, 6046, 6081, 6082, 6117, 6193, 6283, 6371, 6411,
6423, 6514, 6515, 6527, 6541, 6542, 6593, 6635, 6649, 6683, 6694, 6905, 7251, 7291, 7363,
7387, 8023, 8102, 8153, 8203, 8401, 8402, 8403, 8503, 8531, 9019, 9201, 9223, 9271, 9902
		

Crossrefs

Cf. A033548, A046328