A281526 Least number k such that 2*k+n | sigma(k) + sigma(k+n), -1 if such a number is unknown.

672, 12, 42, 748, 75, 364, 5, 332, 45, 10, 13, 112, 312, 26, 30, 3604, 3, 3952, 21, 3780, 24, 6, 55906105, 12000, 3192, 44, 1098, 40, 11, 32123069025, 269, 12, 45, 22, 61, 532, 84660, 76, 1044, 70, 13

Offset

1,1

Comments

In the first 100 terms, the values of a(42), a(54), a(66) and a(78) are greater than 2.5 * 10^11, if they exist. [Giovanni Resta, Jan 24 2017]

Links

Table of n, a(n) for n=1..41.

Paolo P. Lava, First 100 values of n, k, [sigma(k)+sigma(k+n)]/(2*k+n)

Example

For n = 1 -> [sigma(672) + sigma(672+1)] / (672 + 672 + 1) = [2016 + 674] / 1345 = 2690 / 1345 = 2 and 672 is the least number to have this property.

Maple

with(numtheory): P:=proc(q) local a; global n, k;
for n from 1 to q do for k from 1 to q do a:=sigma(k)+sigma(k+n);
if type(a/(2*k+n), integer) then print(k); break; fi; if k=q then print(-1); fi; od; od; end: P(10^6);

Crossrefs

Cf. A000203.

Sequence in context: A172963 A351668 A218795 * A053085 A057695 A233315

Adjacent sequences: A281523 A281524 A281525 * A281527 A281528 A281529

Keyword

sign,more

Author

Paolo P. Lava, Jan 23 2017

Extensions

a(23), a(30), a(49) from Giovanni Resta, Jan 24 2017

Status

approved