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

1,1

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

Links

Table of n, a(n) for n=1..46.

Example

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

Sequence in context: A041402 A041929 A341242 * A041408 A041406 A041410

Adjacent sequences: A174921 A174922 A174923 * A174925 A174926 A174927

Keyword

base,nonn,less

Author

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

Status

approved