cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A333967 Subsequence of A071395. The extra constraint is m is not a term if m*q/p is abundant where prime p|m and q is the least prime larger than p.

Original entry on oeis.org

70, 2002, 3230, 4030, 5830, 8415, 8925, 20482, 32445, 45885, 51765, 83265, 107198, 131054, 133042, 178486, 206770, 253270, 253946, 258970, 270470, 310930, 330310, 334305, 362710, 442365, 474045, 497835, 513890, 544310, 567765, 589095, 592670, 602175, 617265, 631670, 654675
Offset: 1

Views

Author

David A. Corneth, Jul 05 2020

Keywords

Examples

			70 is in the sequence as it's abundant. Its prime factorization is 2 * 5 * 7. Each of 3 * 5 * 7, 2 * 7 * 7 and 2 * 5 * 11 are deficient and no divisor of 70 is in this sequence.
		

Crossrefs

Programs

  • Mathematica
    primabQ[n_] := DivisorSigma[1, n] > 2n && AllTrue[Most @ Divisors[n], DivisorSigma[1, #] < 2# &]; seqQ[n_] := Module[{f = FactorInteger[n]}, p = f[[;; , 1]]; e = f[[;; , 2]]; q = NextPrime[p]; AllTrue[n*(q/p), DivisorSigma[1, #] <= 2# &]]; Select[Range[10^5], primabQ[#] && seqQ[#] &] (* Amiram Eldar, Jul 05 2020 *)