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A174924 Semiprimes sp(k) = q * r such that sum of digits of sp(k) equals sum of digits of the semiprime index k. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 27 10:28 EDT 2021. Contains 347689 sequences. (Running on oeis4.)