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 A097393 Emirpimes: numbers n such that n and its reversal are distinct semiprimes. 30
 15, 26, 39, 49, 51, 58, 62, 85, 93, 94, 115, 122, 123, 129, 143, 155, 158, 159, 169, 177, 178, 183, 185, 187, 203, 205, 221, 226, 265, 289, 302, 314, 319, 321, 326, 327, 329, 335, 339, 341, 355, 381, 394, 398, 413, 415, 437, 493, 497, 502, 511, 514, 533 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Computed by Eric W. Weisstein, Aug 13 2004. LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 Eric Weisstein's World of Mathematics, Emirpimes EXAMPLE 26 is a semiprime, as it is 2 * 13, and so is 62 = 2 * 31. 26 and 62 are therefore both in the sequence. MAPLE isA097393 := proc(n) local R ; R := digrev(n) ; if R <> n then if numtheory[bigomega](R) = 2 and numtheory[bigomega](n) = 2 then return true; else false; end if; else false; end if; end proc: for n from 1 to 500 do if isA097393(n) then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Apr 05 2012 MATHEMATICA Select[Range[500], PrimeOmega[#] == 2 && PrimeOmega[FromDigits[Reverse[IntegerDigits[#]]]] == 2 &] (* Alonso del Arte, Oct 08 2012 *) PROG (PARI) rev(n)=subst(Polrev(digits(n)), 'x, 10) issemi(n)=bigomega(n)==2 list(lim)=my(v=List(), r); forprime(p=2, lim\2, forprime(q=2, min(lim\p, p), r=rev(p*q); if(issemi(r)&&r!=p*q, listput(v, p*q)))); Set(v) \\ Charles R Greathouse IV, Jan 27 2015 (Python) from sympy import factorint from itertools import islice def sp(n): f = factorint(n); return sum(f[p] for p in f) == 2 def ok(n): r = int(str(n)[::-1]); return r != n and sp(n) and sp(r) print([k for k in range(534) if ok(k)]) # Michael S. Branicky, Jul 03 2022 CROSSREFS Cf. A001358, A097394. Sequence in context: A189045 A032609 A050699 * A050700 A263108 A274182 Adjacent sequences: A097390 A097391 A097392 * A097394 A097395 A097396 KEYWORD nonn,base AUTHOR STATUS approved

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Last modified December 6 01:03 EST 2022. Contains 358594 sequences. (Running on oeis4.)