

A085876


Smallest k such that k and k+n have the same prime signature that is different from all previous terms.


2



2, 18, 35, 66, 4, 84, 344, 1692, 1785, 270, 4293, 1176, 9315, 1458, 3450, 5304, 2656, 10332, 8, 1352, 13344, 73040, 190762, 28812, 128180, 77248, 51948, 43092, 196, 35880, 287469, 85968, 387552, 83072, 412300, 45864, 247131
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OFFSET

1,1


LINKS

Table of n, a(n) for n=1..37.


EXAMPLE

a(1) = 2, as 2 and 2+1 = 3 both are primes.
a(2) = 18, 18 and 18+2 = 20 have the prime signature p^2*q.
a(4) = 66 as 66 + 4 = 70, both have prime signature p*q*r which has not occurred earlier.
a(19) = 8 as 8+19 = 27 and 8 and 27 have the same prime signature p^3.


PROG

(PARI) used = vector(42); ps(n) = local(f); f = factor(n); vecsort(f[, 2]); a(n) = local(P, m, v, found, j); P = vector(n, i, ps(i)); m = 1; while (1, for (i = 1, n, v = ps(m*n + i); if (v == P[i], found = 0; j = 1; while (!found && j < n, if (v == used[j], found = 1, j++)); if (!found, used[n] = v; return((m  1)*n + i))); P[i] = v); m++); for (i = 1, 42, c = a(i); print(c)); (Wasserman)


CROSSREFS

Cf. A086489.
Sequence in context: A166259 A073213 A086490 * A099904 A137308 A050594
Adjacent sequences: A085873 A085874 A085875 * A085877 A085878 A085879


KEYWORD

nonn


AUTHOR

Amarnath Murthy, Jul 07 2003


EXTENSIONS

More terms from Ray Chandler, Jul 11 2003
More terms from Ray Chandler, Jul 13 2003


STATUS

approved



