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 A106551 a(n) = n-th semiprime + (concatenation of its two divisors, largest divisor first). 1
 26, 38, 42, 62, 86, 68, 94, 134, 80, 158, 146, 206, 110, 230, 172, 278, 126, 224, 170, 250, 350, 374, 200, 302, 446, 194, 494, 260, 518, 380, 228, 406, 566, 290, 638, 484, 350, 710, 296, 1232, 734, 536, 562, 330, 806, 614, 854, 1454, 440, 878, 470, 950, 692 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Concatenation of the divisors starting with the smallest one leads to a different sequence. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE First semiprime is 4; 4 is 2*2; 26=4+22. Second semiprime is 6; 6 is 3*2; 38=6+32. Third semiprime is 9; 9 is 3*3; 42=9+33. Fourth semiprime is 10; 10 is 5*2; 62=10+52. MAPLE N:= 1000: # for terms <= N Primes:= select(isprime, [2, seq(i, i=3..N/2, 2)]): R:= NULL: for i from 1 to nops(Primes) do for j from 1 to i while Primes[i]*Primes[j] <= N do   R:= R, [Primes[i]*Primes[j], Primes[i]*10^(1+ilog10(Primes[j]))+Primes[j]] od od: map(convert, sort([R], (x, y) -> x

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Last modified October 24 19:40 EDT 2020. Contains 338009 sequences. (Running on oeis4.)