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A247396 Number of even numbers in classes of classification of the positive numbers defined in comment in A247395. 5
0, 1, 3, 8, 12, 36, 24, 60, 36, 84, 156, 60, 204, 156, 84, 180, 300, 336, 120, 384, 276, 144, 456, 324, 516, 744, 396, 204, 420, 216, 444, 1680, 516, 804, 276, 1440, 300, 924, 960, 660, 1020, 1056, 360, 1860, 384, 780, 396, 2460, 2604, 900, 456, 924, 1416, 480 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

In the classification every class contains no more than a finite number of numbers with a given least prime divisor.

LINKS

Indranil Ghosh, Table of n, a(n) for n = 0..1000

Vladimir Shevelev, A classification of the positive integers over primes

FORMULA

For n>=3, a(n) = (prime(n)^2 - prime(n-1)^2)/2.

EXAMPLE

a(6) = (prime(6)^2 - prime(5)^2)/2 = (13^2 - 11^2)/2 = 24. - Indranil Ghosh, Mar 08 2017

MAPLE

A247396:=n->(ithprime(n)^2 - ithprime(n-1)^2)/2: 0, 1, 3, seq(A247396(n), n=3..100); # Wesley Ivan Hurt, Apr 18 2017

MATHEMATICA

a[0] = 0; a[1] = 1; a[2] = 3; a[n_] := (Prime[n]^2 - Prime[n - 1]^2) / 2; Table[a[n], {n, 0, 53}] (* Indranil Ghosh, Mar 08 2017 *)

PROG

(PARI) for(n=0, 53, print1(if(n>2, (prime(n)^2 - prime(n - 1)^2)/2, if(n<2, n, 3)), ", ")) \\ Indranil Ghosh, Mar 08 2017

CROSSREFS

Cf. A000040, A156759, A247393, A247394, A247395.

Sequence in context: A032217 A032142 A032046 * A180507 A218889 A131213

Adjacent sequences:  A247393 A247394 A247395 * A247397 A247398 A247399

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Sep 16 2014

EXTENSIONS

More terms from Peter J. C. Moses, Sep 17 2014

STATUS

approved

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Last modified May 26 09:27 EDT 2019. Contains 323579 sequences. (Running on oeis4.)