A355710 Numbers k such that k and k+1 have the same number of 5-smooth divisors.

2, 21, 33, 34, 38, 57, 85, 86, 93, 94, 104, 116, 122, 141, 145, 146, 154, 158, 171, 177, 182, 189, 201, 205, 213, 214, 218, 237, 265, 266, 273, 296, 302, 321, 326, 332, 334, 338, 344, 357, 362, 381, 385, 387, 393, 394, 398, 417, 445, 446, 453, 454, 475, 476, 482

Offset

1,1

Comments

Numbers k such that A355583(k) = A355583(k+1).

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

2 is a term since A355583(2) = A355583(3) = 2.

Mathematica

s[n_] := Times @@ (1 + IntegerExponent[n, {2, 3, 5}]); Select[Range[500], s[#] == s[#+1] &]

Prog

(PARI) s(n) = (valuation(n, 2) + 1) * (valuation(n, 3) + 1) * (valuation(n, 5) + 1);
s1 = s(1); for(k = 2, 500, s2 = s(k); if(s1 == s2, print1(k-1, ", ")); s1 = s2);

Crossrefs

Cf. A355583, A355709 (3-smooth analog).

Subsequences: A355711, A355712.

Similar sequences: A005237, A006049, A332386, A343819, A344312, A344313, A344314, A348345.

Sequence in context: A071761 A101316 A006920 * A089558 A266873 A215753

Adjacent sequences: A355707 A355708 A355709 * A355711 A355712 A355713

Keyword

nonn

Author

Amiram Eldar, Jul 15 2022

Status

approved