

A086489


Smallest k such that k and k + n have the same prime signature.


4



2, 3, 2, 3, 2, 5, 14, 3, 2, 3, 2, 5, 21, 3, 2, 3, 2, 5, 8, 3, 2, 7, 10, 5, 10, 3, 2, 3, 2, 7, 15, 5, 6, 3, 2, 5, 14, 3, 2, 3, 2, 5, 14, 3, 2, 7, 10, 5, 6, 3, 2, 6, 21, 5, 10, 3, 2, 3, 2, 7, 21, 5, 6, 3, 2, 5, 10, 3, 2, 3, 2, 7, 14, 5, 10, 3, 2, 5, 6, 3, 2, 7, 10, 5, 6, 3, 2, 6, 6, 7, 15, 5, 22, 3, 2, 5, 14
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OFFSET

1,1


LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..20000


EXAMPLE

a(7) = 14 as 14 and 14+7 = 21 have the same prime signature p*q.
a(13) = 21 as 21 is the smallest number such that 21 +13 = 34 and 21 both have the same prime signature p*q.
a(19) = 8 as 8 +19 = 27 = 3^3,8 = 2^3 both have the prime signature p^3.


PROG

(PARI) ps(n) = local(f); f = factor(n); vecsort(f[, 2]); a(n) = local(P, m, v); P = vector(n, i, ps(i)); m = 1; while (1, for (i = 1, n, v = ps(m*n + i); if (v == P[i], return((m  1)*n + i), P[i] = v)); m++); \\ David Wasserman, Mar 09 2005


CROSSREFS

Cf. A085072, A085876.
Sequence in context: A251103 A065559 A087317 * A015886 A255354 A318620
Adjacent sequences: A086486 A086487 A086488 * A086490 A086491 A086492


KEYWORD

nonn


AUTHOR

Amarnath Murthy, Jul 28 2003


EXTENSIONS

More terms from David Wasserman, Mar 09 2005


STATUS

approved



