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A079551 a(n) = Sum_{primes p <= n } d(p-1), where d() = A000005. 2
0, 0, 1, 3, 3, 6, 6, 10, 10, 10, 10, 14, 14, 20, 20, 20, 20, 25, 25, 31, 31, 31, 31, 35, 35, 35, 35, 35, 35, 41, 41, 49, 49, 49, 49, 49, 49, 58, 58, 58, 58, 66, 66, 74, 74, 74, 74, 78, 78, 78, 78, 78, 78, 84, 84, 84, 84, 84, 84, 88, 88, 100, 100, 100, 100, 100, 100, 108, 108, 108, 108 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

REFERENCES

D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, p. 49.

LINKS

Table of n, a(n) for n=0..70.

E. C. Titchmarsh, A divisor problem, Rendiconti del Circolo Matematico di Palermo (1884-1940), December 1930, Volume 54, Issue 1, pp. 414-429.

FORMULA

Several asymptotic estimates are known: see Mitrinovic.

MATHEMATICA

a[n_] := Sum[DivisorSigma[0, p-1], {p, Select[Range[n], PrimeQ]}]; Table[a[n], {n, 0, 100}] (* Jean-Fran├žois Alcover, Nov 26 2015 *)

PROG

(PARI) a(n) = sum(p=1, n, if (isprime(p), numdiv(p-1))); \\ Michel Marcus, Aug 03 2018

CROSSREFS

Cf. A000005, A079552.

Row sums of triangle A143540. [Gary W. Adamson, Aug 23 2008]

Sequence in context: A168237 A290966 A049318 * A182843 A008805 A188270

Adjacent sequences:  A079548 A079549 A079550 * A079552 A079553 A079554

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jan 24 2003

STATUS

approved

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Last modified March 18 17:51 EDT 2019. Contains 321292 sequences. (Running on oeis4.)