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A085774
Numbers k such that (k / sum of digits of k) and (k+1 / sum of digits of k+1) are both semiprime.
0
80, 440, 735, 1014, 1160, 1274, 1547, 2023, 2820, 4806, 5490, 5565, 5875, 6137, 7215, 7748, 10309, 10520, 12104, 12255, 12256, 12257, 12614, 13112, 13481, 14120, 14415, 14705, 14927, 15317, 16434, 17118, 20174, 20175, 20538, 20604, 20804, 21307
OFFSET
1,1
COMMENTS
Note the quadruple: 12255,12256,12257,12258 and the triple: 20174,20175,20176. Conjecture: sequence is infinite.
MATHEMATICA
SequencePosition[Table[PrimeOmega[n/Total[IntegerDigits[n]]], {n, 22000}], {2, 2}][[;; , 1]] (* Harvey P. Dale, Mar 18 2023 *)
PROG
(PARI) isA085772(k)={my(t=k/sumdigits(k)); !frac(t) && bigomega(t)==2}
isok(k)={isA085772(k) && isA085772(k+1)} \\ Andrew Howroyd, Sep 18 2024
CROSSREFS
Cf. A085772.
Sequence in context: A273292 A234333 A234326 * A233353 A233354 A200432
KEYWORD
base,nonn
AUTHOR
Jason Earls, Jul 23 2003
EXTENSIONS
Offset changed by Andrew Howroyd, Sep 18 2024
STATUS
approved