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A160690 a(1)=1. a(n) = the smallest integer > a(n-1) such that d(a(n)) = d(a(n) - a(n-1)), where d(m) = the number of divisors of m. 5
1, 3, 5, 7, 15, 17, 19, 27, 29, 31, 39, 41, 43, 51, 53, 74, 79, 85, 91, 106, 109, 115, 123, 129, 131, 141, 153, 159, 171, 173, 183, 205, 213, 219, 253, 259, 265, 287, 295, 301, 309, 311, 313, 319, 327, 335, 337, 343, 358, 389, 395, 397, 403, 411, 417, 419, 421 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) - A160690(n-1) = A160689(n), for n >= 2.

d(A160689(n)) = d(a(n)) = A160691(n).

LINKS

Michel Marcus, Table of n, a(n) for n = 1..5000

MATHEMATICA

a[1] = 1; a[n_] := a[n] = (For[m = a[n - 1] + 1, DivisorSigma[0, m] != DivisorSigma[0, m - a[n - 1]], m++]; m); Table[a[n], {n, 57}] (* Farideh Firoozbakht, May 28 2009 *)

PROG

(PARI) lista(nn) = {k = 1; print1(k, ", "); last = k; for (n=2, nn, k = last+1; while(numdiv(k) != numdiv(k - last), k++); print1(k, ", "); s += k; last = k; ); } \\ Michel Marcus, Sep 05 2017

CROSSREFS

Cf. A160689, A160691.

Sequence in context: A002181 A073692 A132012 * A085494 A029460 A277910

Adjacent sequences:  A160687 A160688 A160689 * A160691 A160692 A160693

KEYWORD

nonn

AUTHOR

Leroy Quet, May 24 2009

EXTENSIONS

More terms from Farideh Firoozbakht, May 28 2009

STATUS

approved

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Last modified November 18 14:10 EST 2017. Contains 294892 sequences.