A383469 Semiprimes k such that A001358(k) + k and A001358(k) - k are also semiprimes.

4, 6, 46, 55, 87, 93, 94, 206, 298, 326, 362, 382, 394, 542, 562, 629, 758, 841, 866, 926, 993, 1046, 1079, 1147, 1167, 1234, 1317, 1469, 1477, 1561, 1774, 1895, 2047, 2227, 2245, 2515, 2638, 2705, 2894, 2902, 3007, 3031, 3063, 3202, 3269, 3409, 3453, 3466, 3487, 3809, 3891, 4058, 4174, 4207

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

A001358(a(k)) = A383468(k).

Example

a(3) = 46 is a term because 46 = 2 * 23 is a semiprime, A001358(46) = 141, and 141 - 46 = 95 = 5 * 19 and 141 + 46 = 187 = 11 * 17 are semiprimes.

Maple

k:= 0: K:= NULL: count:= 0:
for s from 1 while count < 100 do
  if numtheory:-bigomega(s) = 2 then
    k:= k+1;
    if andmap(t -> numtheory:-bigomega(t) = 2, [k, s-k, s+k]) then
      K:= K, k; count:= count+1;
    fi
  fi;
od:
K;

Crossrefs

Cf. A001358, A383468.

Sequence in context: A012935 A013166 A174653 * A274215 A119944 A338814

Adjacent sequences: A383466 A383467 A383468 * A383470 A383471 A383472

Keyword

nonn

Author

Zak Seidov and Robert Israel, Apr 27 2025

Status

approved