A017294 -id:A017294 - cp's OEIS frontend

A346651 a(n) is the number of divisors of A139245(n) ending with 2.

1, 2, 2, 2, 3, 2, 2, 3, 2, 2, 3, 3, 2, 4, 2, 2, 3, 2, 3, 4, 2, 2, 3, 2, 3, 5, 2, 3, 3, 2, 2, 4, 3, 2, 3, 4, 2, 4, 2, 3, 3, 2, 2, 5, 3, 2, 6, 2, 2, 4, 2, 3, 3, 3, 2, 4, 2, 4, 3, 3, 3, 5, 2, 2, 3, 2, 2, 7, 4, 2, 4, 2, 2, 4, 3, 3, 3, 2, 3, 6, 2, 3, 3, 4, 2, 4, 2, 2, 5, 2

Offset: 1

Stefano Spezia, Jul 26 2021

a(n) is odd if and only if A139245(n) either is the square of a number ending with 2 or has a unitary prime divisor ending with 7.

The term 1 appears only for n = 1 in corresponding to A139245(1) = 4.

			a(14) = 4 since there are 4 divisors of A139245(14) = 264 ending with 2: 2, 12, 22 and 132.

Cf. A000005, A017293 (numbers ending with 2), A017294 (squares of numbers ending with 2), A030432, A056169, A139245 (product of two numbers ending with 2), A346388, A346389.

a[n_]:=Length[Drop[Select[Divisors[20n-16], (Last[IntegerDigits[#]]==2&)]]]; Array[a, 90]

a(n) = sumdiv(20*n-16, d, (d%10) == 2); \\ Michel Marcus, Jul 26 2021

cp's OEIS Frontend

A346651 a(n) is the number of divisors of A139245(n) ending with 2.

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