A369972 - OEIS

A369972

Numbers k such that (prime(k)#)' is a multiple of prime(1+k), where prime(k)# means the k-th primorial, A002110(k), and ' stands for taking the arithmetic derivative, A003415.

0, 2, 7, 14, 21, 28, 261202

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OFFSET

1,2

COMMENTS

Numbers k for which A024451(k) is a multiple of A000040(1+k).

LINKS

Table of n, a(n) for n=1..7.

Index entries for sequences related to primorial numbers

FORMULA

a(n) = A000720(A293457(n)) - 1.

EXAMPLE

7 is included because the primorial prime(7)# = A002110(7) = 510510 has as its arithmetic derivative 510510' = A024451(7) = 716167 = 19*37693, which is divisible by the next larger prime not present in the primorial, in this case by prime(8) = 19.

PROG

(PARI)

A024451(n) = numerator(sum(i=1, n, 1/prime(i)));

isA369972(n) = !(A024451(n)%prime(1+n));

CROSSREFS

Cf. A000040, A000720, A024451, A293457 (corresponding primes), A369970, A369973 (corresponding primorials).

Cf. also A109628.

Sequence in context: A263398 A161702 A114346 * A325159 A087324 A340664

Adjacent sequences: A369969 A369970 A369971 * A369973 A369974 A369975

KEYWORD

nonn,more,hard

AUTHOR

Antti Karttunen, Feb 07 2024

EXTENSIONS

Found a(7) by computing it as A000720(A293457(7))-1. - Antti Karttunen, Feb 08 2024

STATUS

approved