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A002745
Sum of logarithmic numbers.
(Formerly M3909 N1604)
7
1, 5, 20, 96, 469, 3145, 20684, 173544, 1557105, 16215253, 159346604, 2230085528, 26985045333, 368730610729, 5628888393652, 97987283458928, 1475486672174337, 29097611462122437, 505383110562327268, 10970329921706735216
OFFSET
1,2
REFERENCES
J. M. Gandhi, On logarithmic numbers, Math. Student, 31 (1963), 73-83.
Jeffrey Shallit, personal communication.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
J. M. Gandhi, On logarithmic numbers, Math. Student, 31 (1963), 73-83. [Annotated scanned copy]
J. M. Gandhi, Logarithmic Numbers and the Functions d(n) and sigma(n), The American Mathematical Monthly, Vol. 73, No. 9 (1966), pp. 959-964, alternative link.
FORMULA
a(n) = Sum_{k=1..n} A000203(k)*(k-1)!*binomial(n, k). - Vladeta Jovovic, Feb 09 2003
E.g.f.: exp(x) * Sum_{k>=1} x^k / (k*(1 - x^k)). - Ilya Gutkovskiy, Dec 11 2019
a(p) == -1 (mod p) for prime p. The pseudoprimes of this congruence are 30, 858, 1722, ... - Amiram Eldar, May 13 2020
MATHEMATICA
Table[Sum[Binomial[n, k] * DivisorSigma[1, k] * (k-1)!, {k, 1, n}], {n, 1, 20}] (* Vaclav Kotesovec, Dec 16 2019 *)
PROG
(PARI) a(n) = sum(k=1, n, sigma(k)*(k-1)!*binomial(n, k)); \\ Michel Marcus, May 13 2020
CROSSREFS
Sequence in context: A352149 A196532 A377152 * A182959 A224661 A357786
KEYWORD
nonn
EXTENSIONS
More terms from Vladeta Jovovic, Feb 09 2003
STATUS
approved