A392123 Numbers k such that (t(k) - greatest prime < t(k)) < (-t(k) + least prime > t(k)), where t(k) = A000217(k).

2, 10, 13, 17, 22, 29, 32, 34, 36, 37, 45, 49, 58, 61, 62, 65, 70, 73, 77, 86, 90, 91, 94, 97, 103, 105, 106, 108, 109, 110, 114, 118, 120, 123, 127, 130, 134, 138, 141, 142, 144, 151, 154, 157, 166, 177, 182, 183, 188, 190, 192, 193, 197, 198, 199, 201, 204

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..10431

Mathematica

f[x_] := f[x] = (x^2 + x)/2;
u[n_] := NextPrime[f[n], -1]; v[n_] := NextPrime[f[n]];
s1 = Select[Range[1000], f[#] - v[#] < u[#] - f[#] &]   (* A392123 *)

Prog

(Magma) f := func<n | (n^2 + n) div 2>; s1 := [ n : n in [1..300] | f(n) ge 3 and f(n) - NextPrime(f(n)) lt PreviousPrime(f(n)) - f(n)]; s1; // Vincenzo Librandi, Feb 13 2026

Crossrefs

Cf. A000217, A390788, A392125.

Sequence in context: A298000 A058216 A297998 * A037386 A250187 A062317

Adjacent sequences: A392120 A392121 A392122 * A392124 A392125 A392126

Keyword

nonn

Author

Clark Kimberling, Jan 26 2026

Status

approved