login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 11 19:49 EDT 2021. Contains 342888 sequences. (Running on oeis4.)