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A355709
Numbers k such that k and k+1 have the same number of 3-smooth divisors.
2
2, 14, 21, 33, 38, 44, 50, 57, 69, 74, 80, 86, 93, 99, 105, 110, 116, 122, 129, 135, 141, 146, 158, 165, 171, 177, 182, 194, 201, 213, 218, 230, 237, 249, 254, 260, 266, 273, 285, 290, 296, 302, 309, 315, 321, 326, 332, 338, 345, 357, 362, 374, 381, 387, 393, 398
OFFSET
1,1
COMMENTS
Numbers k such that A072078(k) = A072078(k+1).
This sequence is infinite since it includes all the numbers of the form 3*(2^(2*k+1)-1), with k>=1.
LINKS
EXAMPLE
2 is a term since A072078(2) = A072078(3) = 2.
MATHEMATICA
s[n_] := Times @@ (1 + IntegerExponent[n, {2, 3}]); Select[Range[400], s[#] == s[#+1] &]
PROG
(PARI) s(n) = (valuation(n, 2) + 1) * (valuation(n, 3) + 1);
s1 = s(1); for(k = 2, 400, s2 = s(k); if(s1 == s2, print1(k-1, ", ")); s1 = s2);
CROSSREFS
Cf. A072078, A355710 (5-smooth analog).
Sequence in context: A280074 A359745 A086263 * A335071 A073143 A066613
KEYWORD
nonn
AUTHOR
Amiram Eldar, Jul 15 2022
STATUS
approved